@article{lavoie_rojas_khan_shim_2024, title={Charge Protection in Electret Air Filtration Nonwoven Materials}, volume={4}, ISSN={["2365-709X"]}, url={https://doi.org/10.1002/admt.202301670}, DOI={10.1002/admt.202301670}, abstractNote={Abstract}, journal={ADVANCED MATERIALS TECHNOLOGIES}, author={Lavoie, Joseph and Rojas, Orlando J. and Khan, Saad A. and Shim, Eunkyoung}, year={2024}, month={Apr} } @article{sarker_su_rojas_khan_2024, title={Colloidal interactions between nanochitin and surfactants: Connecting micro- and macroscopic properties by isothermal titration calorimetry and rheology}, volume={341}, ISSN={["1879-1344"]}, DOI={10.1016/j.carbpol.2024.122341}, abstractNote={This study elucidates the intricate interactions between chitin nanocrystals (ChNC) and surfactants of same hydrophobic tail (C12) but different head groups types (anionic, cationic, nonionic): sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and polyoxyethylene(23)lauryl ether (Brij-35). Isothermal Titration Calorimetry (ITC) and rheology are used to study the complex ChNC-surfactant interactions in aqueous media, affected by adsorption, self-assembly and micellization. The ITC results demonstrate that the surfactant head group significantly influences the dynamics and nature of the involved phenomena. Cationic DTAB's reveal minimal interaction with ChNC, non-ionic Brij-25's interact moderately at low concentrations driven by hydrophobic effects while SDS's interacts strongly and show complex interaction patterns that fall across four distinct regimes with SDS addition. We attribute such behavior to initiate through electrostatic attraction and terminate in surfactant micelle formation on ChNC surfaces. ITC also elucidates the impact of ChNC concentration on key parameters including critical aggregation concentration (CAC) and saturation concentration (C2). Dynamic rheological analysis indicates the molecular interactions translate to non-linear variations in the elastic modulus (G') upon SDS addition mirroring that observed in ITC experiments. Such a direct correlation between molecular interactions and macroscopic rheological properties provides insights to aid in the creation of nanocomposites with tailored properties.}, journal={CARBOHYDRATE POLYMERS}, author={Sarker, Prottasha and Su, Xiaoya and Rojas, Orlando J. and Khan, Saad A.}, year={2024}, month={Oct} } @article{ebrahim_rahmanian_abdelmigeed_pirzada_khan_2024, title={Designing a MOF-functionalized Nanofibrous Aerogel via Vapor-Phase Synthesis}, volume={5}, ISSN={["2366-9608"]}, url={https://doi.org/10.1002/smtd.202400596}, DOI={10.1002/smtd.202400596}, abstractNote={Designing 3D mechanically robust and high-surface-area substrates for uniform and high-density deposition of metal-organic frameworks (MOFs) provide a promising strategy to enhance surface accessibility and application of these highly functional materials. Nanofibrous aerogel (NFA) with its highly porous self-supported structure composed of interconnected nanofibrous network offers an ideal platform in this regard. Herein, a facile one-pot strategy is introduced, which utilizes direct deposition of MOF on the nanofibrous surface of the NFAs. NFAs are synthesized using electrospun polyacrylonitrile/polyvinylpyrrolidone (PAN/PVP) polymer nanofibers containing zinc acetate (Zn(Ac)}, journal={SMALL METHODS}, author={Ebrahim, Muhammed Ziauddin Ahmad and Rahmanian, Vahid and Abdelmigeed, Mai and Pirzada, Tahira and Khan, Saad A.}, year={2024}, month={May} } @article{jani_farias_jain_houston_velev_santiso_hsiao_khan_2024, title={Isothermal Titration Calorimetry Reveals Entropy-Driven Bisphenol A Epoxy Resin Adhesion to Metal Oxide Surfaces}, volume={1}, ISSN={["1520-5835"]}, url={https://doi.org/10.1021/acs.macromol.3c02440}, DOI={10.1021/acs.macromol.3c02440}, abstractNote={Polymer-coated metals are ubiquitous in multiple industries as a corrosion protection strategy. Particularly in food and beverage packaging, bisphenol A (BPA)-based epoxy coatings provide an excellent barrier and strong adhesion to metals. There is, however, a need to design safer, alternative coatings with similar adhesion as BPA-epoxies due to environmental and health concerns associated with BPA. Limited critical information exists on epoxy-metal interactions and the effect of interfacial functional group concentration on overall adhesion due to the constraints of most experimental methods, which typically probe the interface only within a few nanometers in situ. Herein, we use isothermal titration calorimetry (ITC) and molecular dynamics simulations to characterize the thermodynamics of epoxy-metal oxide binding in the liquid phase and identify the influence of epoxy resin structure and metal oxide surface chemistry in dictating the binding process. Across a series of epoxy resins and three metal oxides, we reveal a previously unreported dominant role of entropy in the binding process, primarily facilitated by the release of bound solvent molecules from the epoxy/metal interface with possible contributions from dispersive OH–π interactions between the benzene rings of the resin and the –OH groups on the metal oxide surface. Enthalpy-favored hydrogen bonding between the –OH groups of the resin and the metal oxide plays a supporting role in the binding, with its participation dependent on the interfacial –OH group concentration. ITC therefore offers key molecular insights into the relative functional group contributions to the adhesion mechanism and informs the rational design of next-generation polymer coatings.}, journal={MACROMOLECULES}, author={Jani, Pallav K. and Farias, Barbara V. and Jain, Rakshit Kumar and Houston, Katelyn R. and Velev, Orlin D. and Santiso, Erik E. and Hsiao, Lilian C. and Khan, Saad A.}, year={2024}, month={Jan} } @article{perera_black_islam_ryu_corder_khan_2024, title={Rheological Behavior and Roll Coating Properties of PDMS Enhanced with Multi-Walled Carbon Nanotubes and Fumed Silica}, url={https://doi.org/10.1021/acsaenm.3c00698}, DOI={10.1021/acsaenm.3c00698}, abstractNote={Scalable manufacturing of micro- and nanoscale textured surfaces from polymer composites is desirable in many applications from drag reduction in ship applications to energy-efficient radiative cooling of infrastructure. Creation of such surfaces, however, remains a challenge. By exploiting the ribbing phenomena that arise when viscous forces dominate over surface tension forces, we can create topographic patterns using roll-to-roll manufacturing techniques. In this work, we analyze how the rheology of yield stress fluids impacts the morphology of roll-coated surfaces using polydimethylsiloxane (PDMS) samples enhanced to varying degrees with multiwalled carbon nanotubes (CNTs) and fumed silica. We observe that CNTs increasingly dominate the large amplitude oscillatory shear response of PDMS composites. However, their impact is modified by the presence of fumed silica, which introduces a transition from intracycle strain softening to hardening behavior. The roll coating behavior of these PDMS composites is examined using image processing to link the rheological properties with the resulting surface morphologies, specifically focusing on two parameters defining surface morphology─ribbing wavenumber and branching patterns. While both types of PDMS composites display comparable wavenumbers, they exhibit different degrees of branching. The deviation in branching can be attributed to the intracycle strain hardening behavior seen at low CNT loadings in PDMS composites containing fumed silica. The study provides insights into the interactions occurring between CNTs and fumed silica in PDMS composites and highlights the significance of analyzing rheological parameters that are relevant at the high strains and strain rates experienced during roll coating, advancing our understanding of ribbing stability in yield stress fluids.}, journal={ACS Applied Engineering Materials}, author={Perera, Himendra and Black, Benjamin and Islam, Md D. and Ryu, Jong E. and Corder, Ria D. and Khan, Saad A.}, year={2024}, month={Mar} } @article{liu_sui_harbinson_pudlo_perera_zhang_liu_ku_islam_liu_et al._2023, title={A scalable microstructure photonic coating fabricated by roll-to-roll “defects” for daytime sub-ambient passive radiative cooling}, volume={23}, ISSN={["1530-6992"]}, url={https://doi.org/10.1021/acs.nanolett.3c00111}, DOI={10.1021/acs.nanolett.3c00111}, abstractNote={The deep space's coldness (∼4 K) provides a ubiquitous and inexhaustible thermodynamic resource to suppress the cooling energy consumption. However, it is nontrivial to achieve subambient radiative cooling during daytime under strong direct sunlight, which requires rational and delicate photonic design for simultaneous high solar reflectivity (>94%) and thermal emissivity. A great challenge arises when trying to meet such strict photonic microstructure requirements while maintaining manufacturing scalability. Herein, we demonstrate a rapid, low-cost, template-free roll-to-roll method to fabricate spike microstructured photonic nanocomposite coatings with Al2O3 and TiO2 nanoparticles embedded that possess 96.0% of solar reflectivity and 97.0% of thermal emissivity. When facing direct sunlight in the spring of Chicago (average 699 W/m2 solar intensity), the coatings show a radiative cooling power of 39.1 W/m2. Combined with the coatings' superhydrophobic and contamination resistance merits, the potential 14.4% cooling energy-saving capability is numerically demonstrated across the United States.}, number={17}, journal={Nano Letters}, author={Liu, S. and Sui, C. and Harbinson, M. and Pudlo, M. and Perera, Himendra and Zhang, Zhenzhen and Liu, Ruguan and Ku, Zahyun and Islam, Md Didarul and Liu, Yuxuan and et al.}, editor={Ryu, JongEditor}, year={2023}, pages={7767–7774} } @article{pirzada_khan_opperman_affokpon_2023, title={Banana-paper seed wrap increases yam crop yield and quality in Africa}, volume={2}, ISSN={["2662-1355"]}, DOI={10.1038/s43016-023-00718-9}, journal={NATURE FOOD}, author={Pirzada, Tahira and Khan, Saad A. and Opperman, Charles H. and Affokpon, Antoine}, year={2023}, month={Feb} } @article{sohail_pirzada_guenther_barbieri_sit_menegatti_crook_opperman_khan_2023, title={Cellulose Acetate-Stabilized Pickering Emulsions: Preparation, Rheology, and Incorporation of Agricultural Active Ingredients}, volume={11}, ISSN={["2168-0485"]}, url={https://doi.org/10.1021/acssuschemeng.3c02428}, DOI={10.1021/acssuschemeng.3c02428}, abstractNote={We report the use of cellulose acetate (CA) nanoparticles (NPs) to produce oil in water Pickering emulsions. The CA NP can emulsify various oils and form stable emulsions at concentrations as low as 0.5 wt %. Rheological and microscopic analyses show evidence of interconnected NP aggregate networks between droplets. Yield stress measurements display evidence of “double” yielding. We postulate that the presence of the NP aggregates provides a secondary network between droplet clusters resulting in such behavior. We demonstrate the suitability of the emulsions as agriculture formulations by incorporating an agrochemical, abamectin (Abm), and a plant-growth-promoting microbe (PGPM) in the emulsions. Release assays exhibit sustained Abm release, promising higher efficacy at lower usage volumes. Incorporation of nonsporulating PGPM Pseudomonas simiae in the emulsions shows significantly higher microbe viability compared to controls after 70 days of storage. By demonstrating the application of CA NPs as a sustainable Pickering emulsifier, this study introduces the use of CA as a platform technology for the delivery of diverse agriculture cargos. A comprehensive evaluation of the system is articulated in a fundamental microstructure analysis and a demonstration of practical on-site attributes, including shelf-life stability and functional performance, verified through bioassays and plant growth studies.}, number={42}, journal={ACS SUSTAINABLE CHEMISTRY & ENGINEERING}, author={Sohail, Mariam and Pirzada, Tahira and Guenther, Richard and Barbieri, Eduardo and Sit, Tim and Menegatti, Stefano and Crook, Nathan and Opperman, Charles H. and Khan, Saad A.}, year={2023}, month={Sep}, pages={15178–15191} } @article{nalband_sarker_khan_freytes_2023, title={Characterization and biological evaluation of a novel flavonoid-collagen antioxidant hydrogel with cytoprotective properties}, volume={9}, ISSN={["1552-4981"]}, DOI={10.1002/jbm.b.35321}, abstractNote={Abstract}, journal={JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS}, author={Nalband, Danielle M. and Sarker, Prottasha and Khan, Saad A. and Freytes, Donald O.}, year={2023}, month={Sep} } @article{sarker_jani_hsiao_rojas_khan_2023, title={Interacting collagen and tannic acid Particles: Uncovering pH-dependent rheological and thermodynamic behaviors}, volume={650}, ISSN={0021-9797}, url={http://dx.doi.org/10.1016/j.jcis.2023.06.209}, DOI={10.1016/j.jcis.2023.06.209}, abstractNote={Biomaterials such as collagen and tannic acid (TA) particles are of interest in the development of advanced hybrid biobased systems due to their beneficial therapeutic functionalities and distinctive structural properties. The presence of numerous functional groups makes both TA and collagen pH responsive, enabling them to interact via non-covalent interactions and offer tunable macroscopic properties.The effect of pH on the interactions between collagen and TA particles is explored by adding TA particles at physiological pH to collagen at both acidic and neutral pH. Rheology, isothermal titration calorimetry (ITC), turbidimetric analysis and quartz crystal microbalance with dissipation monitoring (QCM-D) are used to study the effects.Rheology results show significant increase in elastic modulus with an increase in collagen concentration. However, TA particles at physiological pH provide stronger mechanical reinforcement to collagen at pH 4 than collagen at pH 7 due to the formation of a higher extent of electrostatic interaction and hydrogen bonding. ITC results confirm this hypothesis, with larger changes in enthalpy, |ΔH|, observed when collagen is at acidic pH and |ΔH| > |TΔS| indicating enthalpy-driven collagen-TA interactions. Turbidimetric analysis and QCM-D help to identify structural differences of the collagen-TA complexes and their formation at both pH conditions.}, journal={Journal of Colloid and Interface Science}, publisher={Elsevier BV}, author={Sarker, Prottasha and Jani, Pallav K. and Hsiao, Lilian C. and Rojas, Orlando J. and Khan, Saad A.}, year={2023}, month={Nov}, pages={541–552} } @article{corder_vachieri_martin_taylor_fleming_khan_2023, title={Linear and nonlinear rheology of liberase-treated breast cancer tumors}, volume={1}, ISSN={["2047-4849"]}, url={https://doi.org/10.1039/D3BM00038A}, DOI={10.1039/D3BM00038A}, abstractNote={The effects of injectable, localized liberase treatments on the linear and nonlinear rheology of allograft 4T1 mouse mammary tumors are examined, demonstrating how insights about the tumor microenvironment can be gleaned from the rheological data.}, journal={BIOMATERIALS SCIENCE}, author={Corder, Ria D. and Vachieri, Robert B. and Martin, Megan E. and Taylor, Darlene K. and Fleming, Jodie M. and Khan, Saad A.}, year={2023}, month={Jan} } @article{rahmanian_pirzada_barbieri_iftikhar_li_khan_2023, title={Mechanically robust, thermally insulating and photo-responsive aerogels designed from sol-gel electrospun PVP-TiO2 nanofibers}, volume={32}, ISSN={["2352-9407"]}, url={https://doi.org/10.1016/j.apmt.2023.101784}, DOI={10.1016/j.apmt.2023.101784}, abstractNote={We present a robust approach for fabricating polyvinylpyrrolidone (PVP)-titania (TiO2) nanofibrous aerogels (NFA) with multifunctional and triggered performances. These low density (∼ 10 mg cm−3) 3D self-supported aerogels having an intrinsically lamellar porous structure (> 99% porosity) are created via solid templating of sol-gel electrospun PVP-TiO2 hybrid nanofibers. The photocatalytic activity of TiO2 allows for on-demand application wherein the aerogel exhibits antibacterial properties upon UV exposure to bacteria such as Escherichia coli and Salmonella enterica. Significantly, while the aerogel sorbs common volatile organic components (VOCs) or oil due to its innate porosity, exposure of the aerogel to ultraviolet (UV) radiation leads to their decomposition. The PVP-TiO2 NFA exhibits a low thermal conductivity (0.062 W m−1 K−1) together with considerable mechanical flexibility up to strains of 50% with >90% recovery, without the need for post-processing. The photo-responsive attributes combined with mechanical resilience, oleophilicity and thermal insulation properties render these aerogels viable candidates for a diverse range of applications. We discuss such property enhancements in terms of the interaction between PVP and TiO2 and aerogel microstructure.}, journal={APPLIED MATERIALS TODAY}, author={Rahmanian, Vahid and Pirzada, Tahira and Barbieri, Eduardo and Iftikhar, Sherafghan and Li, Fanxing and Khan, Saad A.}, year={2023}, month={Jun} } @article{kotb_serfass_cagnard_houston_khan_hsiao_velev_2023, title={Molecular structure effects on the mechanisms of corrosion protection of model epoxy coatings on metals}, volume={7}, ISSN={2052-1537}, url={http://dx.doi.org/10.1039/d2qm01045c}, DOI={10.1039/D2QM01045C}, abstractNote={We investigate the role of the polymer network structure on the corrosion protection efficiency of thermoset epoxy coatings on metals as a prerequisite for the future design of safer alternatives to bisphenol A-based epoxy resins.}, number={2}, journal={Materials Chemistry Frontiers}, publisher={Royal Society of Chemistry (RSC)}, author={Kotb, Yosra and Serfass, Christopher M. and Cagnard, Alain and Houston, Katelyn R. and Khan, Saad A. and Hsiao, Lilian C. and Velev, Orlin D.}, year={2023}, pages={274–286} } @article{rahmanian_ebrahim_razavi_abdelmigeed_barbieri_menegatti_parsons_li_pirzada_khan_2023, title={Vapor phase synthesis of metal-organic frameworks on a nanofibrous aerogel creates enhanced functionality}, volume={11}, ISSN={["2050-7496"]}, url={https://doi.org/10.1039/D3TA05299K}, DOI={10.1039/D3TA05299K}, abstractNote={Vapor-phase synthesis of metal–organic frameworks (MOFs) on nanofibrous aerogels provides a hierarchically porous and mechanically robust material platform for use in a multitude of applications, from carbon dioxide capture to heavy metal removal.}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, author={Rahmanian, Vahid and Ebrahim, Muhammed Ziauddin Ahmad and Razavi, Seyedamin and Abdelmigeed, Mai and Barbieri, Eduardo and Menegatti, Stefano and Parsons, Gregory N. and Li, Fanxing and Pirzada, Tahira and Khan, Saad A.}, year={2023}, month={Nov} } @book{andrady_khan_2022, place={Hoboken, NJ}, title={Applications of Polymer Nanofibers}, ISBN={9781119267683 9781119267713}, url={http://dx.doi.org/10.1002/9781119267713}, DOI={10.1002/9781119267713}, publisher={Wiley}, year={2022}, month={Feb} } @article{wang_pirzada_xie_barbieri_hossain_opperman_pal_wei_parsons_khan_2022, title={Creating hierarchically porous banana paper-metal organic framework (MOF) composites with multifunctionality}, volume={28}, ISSN={["2352-9407"]}, url={https://doi.org/10.1016/j.apmt.2022.101517}, DOI={10.1016/j.apmt.2022.101517}, abstractNote={We report a robust approach to integrate metal-organic frameworks (MOF) via vapor phase synthesis on a cost-effective and mechanically durable fibrous banana paper (BP) substrate developed from lignocellulosic biomass. The unique hollow fibrous structure of BP combined with the methodology used produces MOF-fiber composites with uniform MOF distribution and enhanced functionalities, with minimal use of organic solvents. The BP-MOF composites demonstrate a high surface area of 552 m2/g and uniform surface growth of MOF on them. Mechanical strength and bending flexibility of the substrate is well retained after the MOF growth, while the hollow tubular nature and hierarchical porosity of the BP facilitate gas diffusion. The BP-MOF composites demonstrate strong antibacterial activity with 99.2% of E.coli destroyed within the first hour of incubation. Preliminary studies with smartphone-based volatile organic compound (VOC) sensor show enhanced 1-octen-3-ol vapor absorption on BP-MOF, indicating its potential for VOC capture and sensing. We believe that the sustainable nature and flexibility of the lignocellulosic BP substrate taken together with uniform growth of MOF on the hierarchically porous BP impart impressive attributes to these composites, which can be explored in diverse applications.}, journal={APPLIED MATERIALS TODAY}, publisher={Elsevier BV}, author={Wang, Siyao and Pirzada, Tahira and Xie, Wenyi and Barbieri, Eduardo and Hossain, Oindrila and Opperman, Charles H. and Pal, Lokendra and Wei, Qingshan and Parsons, Gregory N. and Khan, Saad A.}, year={2022}, month={Aug} } @article{hosseini_rahmanian_pirzada_frick_krissanaprasit_khan_labean_2022, title={DNA aerogels and DNA-wrapped CNT aerogels for neuromorphic applications}, volume={16}, ISSN={["2590-0064"]}, url={https://doi.org/10.1016/j.mtbio.2022.100440}, DOI={10.1016/j.mtbio.2022.100440}, abstractNote={Nucleic acids are programmable materials that can self-assemble into defined or stochastic three-dimensional network architectures. Various attributes of self-assembled, cross-linked Deoxyribonucleic acid (DNA) hydrogels have recently been investigated, including their mechanical properties and potential biomedical functions. Herein, for the first time, we describe the successful construction of pure DNA aerogels and DNA-wrapped carbon nanotube (CNT) composite (DNA-CNT) aerogels via a single-step freeze-drying of the respective hydrogels. These aerogels reveal highly porous and randomly branched structures with low density. The electrical properties of pure DNA aerogel mimic that of a simple capacitor; in contrast, the DNA-CNT aerogel displays a fascinating resistive switching behavior in response to an applied bias voltage sweep reminiscent of a volatile memristor. We believe these novel aerogels can serve as a platform for developing complex biomimetic devices for a wide range of applications, including real-time computation, neuromorphic computing, biochemical sensing, and biodegradable functional implants. More importantly, insight obtained here on self-assembling DNA to create aerogels will pave the way to construct novel aerogel-based material platforms from DNA coated or wrapped functional entities.}, journal={MATERIALS TODAY BIO}, author={Hosseini, Mahshid and Rahmanian, Vahid and Pirzada, Tahira and Frick, Nikolay and Krissanaprasit, Abhichart and Khan, Saad A. and LaBean, Thomas H.}, year={2022}, month={Dec} } @article{black_chockalingam_islam_liu_perera_khan_ryu_2022, title={Fabrication of Bioinspired Micro/Nano-Textured Surfaces Through Scalable Roll Coating Manufacturing}, volume={10}, ISSN={2166-0468 2166-0476}, url={http://dx.doi.org/10.1115/1.4056732}, DOI={10.1115/1.4056732}, abstractNote={Abstract}, number={2}, journal={Journal of Micro and Nano-Manufacturing}, publisher={ASME International}, author={Black, Benjamin and Chockalingam, Sekkappan and Islam, Md Didarul and Liu, Sipan and Perera, Himendra and Khan, Saad and Ryu, Jong Eun}, year={2022}, month={Jun}, pages={021006} } @article{sarker_nalband_freytes_rojas_khan_2022, title={High-Axial-Aspect Tannic Acid Microparticles Facilitate Gelation and Injectability of Collagen-Based Hydrogels}, volume={10}, ISSN={["1526-4602"]}, url={https://doi.org/10.1021/acs.biomac.2c00916}, DOI={10.1021/acs.biomac.2c00916}, abstractNote={Injectable collagen-based hydrogels offer great promise for tissue engineering and regeneration, but their use is limited by poor mechanical strength. Herein, we incorporate tannic acid (TA) to tailor the rheology of the corresponding hydrogels while simultaneously adding the therapeutic benefits inherent to this polyphenolic component. TA in the solution form and needle-shaped TA microparticles are combined with collagen and the respective systems studied for their time-dependent sol-gel transitions (from storage to body temperatures, 4-37 °C) as a function of TA concentration. Compared to systems incorporating TA microparticles, those with dissolved TA, applied at a similar concentration, generate a less significant enhancement of the elastic modulus. Premature gelation at a low temperature and associated colloidal arrest of the system are proposed as a main factor explaining this limited performance. A higher yield stress (elastic stress method) is determined for systems loaded with TA microparticles compared to the system with dissolved TA. These results are interpreted in terms of the underlying interactions of TA with collagen, as probed by spectroscopy and isothermal titration calorimetry. Importantly, hydrogels containing TA microparticles show high cell viability (human dermal fibroblasts) and comparative cellular activity relative to the collagen-only hydrogel. Overall, composite hydrogels incorporating TA microparticles demonstrate a new, simple, and better-performance alternative to cell culturing and difficult implantation scenarios.}, journal={BIOMACROMOLECULES}, author={Sarker, Prottasha and Nalband, Danielle M. and Freytes, Donald O. and Rojas, Orlando J. and Khan, Saad A.}, year={2022}, month={Oct} } @article{mora-navarro_garcia_sarker_ozpinar_enders_khan_branski_freytes_2022, title={Monitoring decellularization via absorbance spectroscopy during the derivation of extracellular matrix scaffolds}, volume={17}, ISSN={["1748-605X"]}, url={https://doi.org/10.1088/1748-605X/ac361f}, DOI={10.1088/1748-605X/ac361f}, abstractNote={Abstract}, number={1}, journal={BIOMEDICAL MATERIALS}, publisher={IOP Publishing}, author={Mora-Navarro, Camilo and Garcia, Mario E. and Sarker, Prottasha and Ozpinar, Emily W. and Enders, Jeffrey R. and Khan, Saad and Branski, Ryan C. and Freytes, Donald O.}, year={2022}, month={Jan} } @article{sattor_pervaje_pasquinelli_khan_santiso_2022, title={Multiscale Constitutive Modeling of the Mechanical Properties of Polypropylene Fibers from Molecular Simulation Data}, volume={1}, ISSN={["1520-5835"]}, url={https://doi.org/10.1021/acs.macromol.1c00630}, DOI={10.1021/acs.macromol.1c00630}, abstractNote={We present a multiscale approach to create a constitutive model that predicts the mechanical properties of polypropylene fibers based on chemical and physical characteristics. The development of this method relies on validation with experimental stress–strain curves from nine different isotactic polypropylene (iPP) fibers with their varying molecular weight characteristics, Hermans orientation factors, and crystallinity. Complementary molecular models were built by using molecular dynamics (MD) simulations with united atom models. Tensile deformation simulations adapting a quasi-static procedure resulted in stress–strain curves that aligned well with the experimentally measured ones. A neural network model was trained on the MD simulation data to create correlations that predict parameters for a chosen constitutive model that describes the mechanical properties of the polypropylene fibers. This computational approach is amenable to be applied to polymer fiber systems and aims to aid in the design of polymeric materials to achieve targeted mechanical properties.}, number={3}, journal={MACROMOLECULES}, publisher={American Chemical Society (ACS)}, author={Sattor, Amulya K. and Pervaje, Amulya K. and Pasquinelli, Melissa A. and Khan, Saad A. and Santiso, Erik E.}, year={2022}, month={Jan} } @article{ramesh_davis_roros_zhou_he_gao_menegatti_khan_genzer_2022, title={Nonwoven Membranes with Infrared Light-Controlled Permeability}, volume={9}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.2c13280}, abstractNote={This study presents the development of the first composite nonwoven fiber mats (NWFs) with infrared light-controlled permeability. The membranes were prepared by coating polypropylene NWFs with a photothermal layer of poly(N-isopropylacrylamide) (PNIPAm)-based microgels impregnated with graphene oxide nanoparticles (GONPs). This design enables "photothermal smart-gating" using light dosage as remote control of the membrane's permeability to electrolytes. Upon exposure to infrared light, the GONPs trigger a rapid local increase in temperature, which contracts the PNIPAm-based microgels lodged in the pore space of the NWFs. The contraction of the microgels can be reverted by cooling from the surrounding aqueous environment. The efficient conversion of infrared light into localized heat by GONPs coupled with the phase transition of the microgels above the lower critical solution temperature (LCST) of PNIPAm provide effective control over the effective porosity, and thus the permeability, of the membrane. The material design parameters, namely the monomer composition of the microgels and the GONP-to-microgel ratio, enable tuning the permeability shift in response to IR light; control NWFs coated with GONP-free microgels displayed thermal responsiveness only, whereas native NWFs showed no smart-gating behavior at all. This technology shows potential toward processing temperature-sensitive bioactive ingredients or remote-controlled bioreactors.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Ramesh, Srivatsan and Davis, Jack and Roros, Alexandra and Zhou, Chuanzhen and He, Nanfei and Gao, Wei and Menegatti, Stefano and Khan, Saad and Genzer, Jan}, year={2022}, month={Sep} } @article{barbieri_cutright_ramesh_khan_efimenko_genzer_menegatti_2022, title={Potent Antibacterial Composite Nonwovens Functionalized with Bioactive Peptides and Polymers}, volume={8}, ISSN={["2196-7350"]}, url={https://doi.org/10.1002/admi.202201061}, DOI={10.1002/admi.202201061}, abstractNote={Abstract}, journal={ADVANCED MATERIALS INTERFACES}, author={Barbieri, Eduardo and Cutright, Camden C. and Ramesh, Srivatsan and Khan, Saad A. and Efimenko, Kirill and Genzer, Jan and Menegatti, Stefano}, year={2022}, month={Aug} } @article{sohail_pirzada_opperman_khan_2022, title={Recent advances in seed coating technologies: transitioning toward sustainable agriculture}, volume={7}, ISSN={["1463-9270"]}, url={https://doi.org/10.1039/D2GC02389J}, DOI={10.1039/D2GC02389J}, abstractNote={This review provides a sustainability perspective on existing seed coating research through comparing potential agricultural benefits with the associated energy, chemical and environmental footprints.}, journal={GREEN CHEMISTRY}, publisher={Royal Society of Chemistry (RSC)}, author={Sohail, Mariam and Pirzada, Tahira and Opperman, Charles H. and Khan, Saad A.}, year={2022}, month={Jul} } @misc{ramesh_khan_park_ford_menegatti_genzer_2022, title={Self-healing and repair of fabrics: A comprehensive review of the application toolkit}, volume={54}, ISSN={["1873-4103"]}, DOI={10.1016/j.mattod.2021.11.016}, abstractNote={Self-healing fabrics respond to chemical and physical damage by restoring functional, structural, and morphological features. We present a comprehensive review of textile hybrids or composites capable of self-healing and repairing fabrics against damages across the micro- (µm), meso- (µm – mm), and macro-scale (>mm). The reviewed literature is organized in three sections presenting (i) the chemistry and fabrication principles of designing self-healing fabrics against increasing size scales of repair, (ii) stimuli-driven and autonomous healing, and (iii) the methods to characterize the recovery of wettability, barrier, morphological, mechanical, and other properties. The discussion of mainstream methods for developing self-healing fabrics focuses on coatings, composites, and specialized fabrication techniques required as the damage size grows from µm to mm to >mm. The section on stimuli-driven repair and autonomous recovery discusses the time scales associated with different damage repair, showing how external stimuli provide a higher driving force towards healing and accelerate material restoration than autonomous recovery. Finally, an array of optical, mechanical, and functional characterization techniques is discussed to evaluate the recovery yield and understand the repair mechanisms of the various fabrics. This review demonstrates the virtually limitless uses of next-generation self-healing systems, from separations to protective clothing, anti-fouling, and self-cleaning.}, journal={MATERIALS TODAY}, author={Ramesh, Srivatsan and Khan, Saad and Park, Yaewon and Ford, Ericka and Menegatti, Stefano and Genzer, Jan}, year={2022}, month={Apr}, pages={90–109} } @article{islam_perera_black_phillips_chen_hodges_jackman_liu_kim_zikry_et al._2022, title={Template‐Free Scalable Fabrication of Linearly Periodic Microstructures by Controlling Ribbing Defects Phenomenon in Forward Roll Coating for Multifunctional Applications}, volume={9}, ISSN={2196-7350 2196-7350}, url={http://dx.doi.org/10.1002/admi.202201237}, DOI={10.1002/admi.202201237}, abstractNote={Abstract}, number={27}, journal={Advanced Materials Interfaces}, publisher={Wiley}, author={Islam, Md Didarul and Perera, Himendra and Black, Benjamin and Phillips, Matthew and Chen, Muh‐Jang and Hodges, Greyson and Jackman, Allyce and Liu, Yuxuan and Kim, Chang‐Jin and Zikry, Mohammed and et al.}, year={2022}, month={Aug}, pages={2201237} } @article{kotb_cagnard_houston_khan_hsiao_velev_2022, title={What makes epoxy-phenolic coatings on metals ubiquitous: Surface energetics and molecular adhesion characteristics}, volume={608}, ISSN={["1095-7103"]}, DOI={10.1016/j.jcis.2021.09.091}, abstractNote={Wetting characteristics of epoxy and phenolic resins on metals depend on the molecular interactions between resins' functional groups and metal surface. Those interactions affect the practical adhesion strength of epoxy-phenolic coatings on metals. Estimation of the theoretical adhesion energies can reveal this system's microscopic adhesion mechanisms.Adhesion is estimated theoretically based on resins' wettability on metals, and experimentally through pull-off adhesion testing of cured coatings. The effect of various functional groups on adhesion is decoupled using epoxy and phenolic resins with different functionalities. To assess the impact of the metal passivation on adhesion, tinplated and tin-free steel substrates are used. Differences in their surface chemical composition and polarity are investigated using XPS.Theoretical adhesion results reveal a superior adhesion of epoxy compared to phenolic resins. Moreover, epoxy resins having a higher content of epoxide-to-hydroxyl groups show improved theoretical and practical adhesion. The importance of epoxides in driving resins' initial adhesion on metals is attributed to the formation of direct chemical bonds with active hydrogen on metal surfaces. The adhesion of coatings on tin-free steel is found to be higher than on tinplated steel. This is associated to the increased hydroxyl fraction on tin-free steel surface leading to more hydrogen bonds formation.}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, author={Kotb, Yosra and Cagnard, Alain and Houston, Katelyn R. and Khan, Saad A. and Hsiao, Lilian C. and Velev, Orlin D.}, year={2022}, month={Feb}, pages={634–643} } @article{ochola_cortada_mwaura_tariku_christensen_ng'ang'a_hassanali_pirzada_khan_pal_et al._2022, title={Wrap-and-plant technology to manage sustainably potato cyst nematodes in East Africa}, volume={2}, ISSN={["2398-9629"]}, url={https://doi.org/10.1038/s41893-022-00852-5}, DOI={10.1038/s41893-022-00852-5}, abstractNote={Abstract}, journal={NATURE SUSTAINABILITY}, author={Ochola, Juliet and Cortada, Laura and Mwaura, Onesmus and Tariku, Meklit and Christensen, Shawn A. and Ng'ang'a, Margaret and Hassanali, Ahmed and Pirzada, Tahira and Khan, Saad and Pal, Lokendra and et al.}, year={2022}, month={Feb} } @article{jin_khan_spontak_rojas_2021, title={Anion-Specific Water Interactions with Nanochitin: Donnan and Osmotic Pressure Effects as Revealed by Quartz Microgravimetry}, volume={37}, ISSN={["0743-7463"]}, url={https://doi.org/10.1021/acs.langmuir.1c01585}, DOI={10.1021/acs.langmuir.1c01585}, abstractNote={The development of new materials emphasizes greater use of sustainable and eco-friendly resources, including those that take advantage of the unique properties of nanopolysaccharides. Advances in this area, however, necessarily require a thorough understanding of interactions with water. Our contribution to this important topic pertains to the swelling behavior of partially deacetylated nanochitin (NCh), which has been studied here by quartz crystal microgravimetry. Ultrathin films of NCh supported on gold-coated resonators have been equilibrated in aqueous electrolyte solutions (containing NaF, NaCl, NaBr, NaNO3, Na2SO4, Na2SO3, or Na3PO4) at different ionic strengths. As anticipated, NCh displays contrasting swelling/deswelling responses, depending on the ionic affinities and valences of the counterions. The extent of water uptake induced by halide anions, for instance, follows a modified Hofmeister series with F– producing the highest swelling. In marked contrast, Cl– induces film dehydration. We conclude that larger anions promote deswelling such that water losses increase with increasing anion valence. Results such as the ones reported here are critical to ongoing efforts designed to dry chitin nanomaterials and develop bio-based and sustainable materials, including particles, films, coatings, and other nanostructured assemblies, for various devices and applications.}, number={38}, journal={LANGMUIR}, publisher={American Chemical Society (ACS)}, author={Jin, Soo-Ah and Khan, Saad A. and Spontak, Richard J. and Rojas, Orlando J.}, year={2021}, month={Sep}, pages={11242–11250} } @article{facchine_bai_rojas_khan_2021, title={Associative structures formed from cellulose nanofibrils and nanochitins are pH-responsive and exhibit tunable rheology}, volume={588}, ISSN={["1095-7103"]}, url={https://doi.org/10.1016/j.jcis.2020.12.041}, DOI={10.1016/j.jcis.2020.12.041}, abstractNote={Nanocellulose and nanochitin are both biobased materials with complementary structures and properties. Both exhibit pH-dependent surface charges which are opposite in sign. Hence, it should be possible to manipulate them to form complexed structures via ionic bond formation at prescribed pH conditions.Nanocellulose and nanochitin were mixed after exposure to acidic or neutral conditions to influence their ionization state. The heat of interaction during the introduction of nanochitin to nanocellulose was monitored via isothermal titration calorimetry. The strength and gel properties of the resulting structures were characterized via rheological measurement.The resultant gel properties in the designed hybrid systems were found to depend directly on the charge state of the starting materials, which was dictated by pH adjustment. Different interparticle interactions including ionic attraction, hydrophobic associations, and physical entanglement were identified in the systems and the influence of each was elucidated for different conditions of pH, concentration, and ratio of nanochitin to nanocellulose. Hydrophobic associations between neutralized nanochitin particles were found to contribute strongly to increased elastic modulus values. Ionic complex formation was found to provide enhanced stability under broader pH conditions, while physical entanglement of cellulose nanofibers was a substantial thickening mechanism in all systems.}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, author={Facchine, Emily G. and Bai, Long and Rojas, Orlando J. and Khan, Saad A.}, year={2021}, month={Apr}, pages={232–241} } @article{jin_facchine_rojas_khan_spontak_2021, title={Cellulose nanofibers and the film-formation dilemma: Drying temperature and tunable optical, mechanical and wetting properties of nanocomposite films composed of waterborne sulfopolyesters}, volume={598}, ISSN={["1095-7103"]}, url={https://doi.org/10.1016/j.jcis.2021.04.032}, DOI={10.1016/j.jcis.2021.04.032}, abstractNote={Waterborne sulfopolyesters have gained considerable interest as coating materials due to their excellent film-forming and optical properties. Their commercial use has been limited, however, due to their fragile nature. Incorporating cellulose nanofiber (CNF), a sustainable biopolymer, into the polymer matrix is expected to enhance the mechanical integrity of the nanocomposite as these two components synergistically interact. In this study, we have investigated the suspension and film characteristics of three sulfopolyesters varying in charge density, glass transition temperature and molecular weight, as well as their mixtures with CNF. We have performed steady-shear rheology on mixtures with different CNF loading levels, and resulting films have been subjected to quasistatic uniaxial tensile and water contact-angle tests to elucidate the effects of CNF on mechanical and surface properties. Addition of CNF to waterborne polyester promotes shear-thinning behavior that remains unaffected by the CNF content. Solid films cast from these suspensions possess enhanced mechanical properties, as well as tailorable surface hydrophilicity, depending on composition and film-drying temperature. Tensile tests reveal that films containing 10 wt% CNF display the greatest mechanical improvements, suggesting the existence of a previously unidentified Goldilocks composition window.}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, publisher={Elsevier BV}, author={Jin, Soo-Ah and Facchine, Emily G. and Rojas, Orlando J. and Khan, Saad A. and Spontak, Richard J.}, year={2021}, month={Sep}, pages={369–378} } @article{rahmanian_pirzada_wang_khan_2021, title={Cellulose-Based Hybrid Aerogels: Strategies toward Design and Functionality}, volume={33}, ISSN={["1521-4095"]}, url={https://doi.org/10.1002/adma.202102892}, DOI={10.1002/adma.202102892}, abstractNote={Abstract}, number={51}, journal={ADVANCED MATERIALS}, publisher={Wiley}, author={Rahmanian, Vahid and Pirzada, Tahira and Wang, Siyao and Khan, Saad A.}, year={2021}, month={Oct} } @article{rutkevicius_pirzada_geiger_khan_2021, title={Creating superhydrophobic, abrasion-resistant and breathable coatings from water-borne polydimethylsiloxane-polyurethane Co-polymer and fumed silica}, volume={596}, ISSN={["1095-7103"]}, url={https://doi.org/10.1016/j.jcis.2021.02.072}, DOI={10.1016/j.jcis.2021.02.072}, abstractNote={The high surface area and branched structure of fumed silica (FS) can be exploited in concert with the hydrophobic properties of polydimethylsiloxane (PDMS) and robustness of polyurethane (PU) to create PDMS-PU and FS grafted coatings with hierarchical structures and enhanced functionalities. The structural features of FS would add to superhydrophobicity; its open-branchlike characteristics would provide air permeability; the use of a tiered coating approach involving a FS-only layer on top of the PDMS-PU coat would create interlocking and strong abrasion-resistance, leading to a multifunctional coating with potential application in filtration and personal protection equipment (PPE). PDMS-PU and PDMS-PU-Si copolymer dispersions are synthesized with different monomer molecular weights and FS concentration. Hydrophobicity is measured via water contact angle and wetting resistance measurements. Abrasion resistance is compared by investigating the fiber morphology and hydrophobicity of the coated fabrics after various abrasion cycles. Air flow versus pressure drop experiments are used to measure breathability. Interaction mechanism between substrate/components are explored using infrared spectroscopy. The interactions between the substrate, FS, and PDMS-PU can be manipulated to create a novel, tiered coating that exhibits superhydrophobicity, strong abrasion resistance together with desirable air-permeability, thereby providing a versatile and unique coating platform.}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, publisher={Elsevier BV}, author={Rutkevicius, Marius and Pirzada, Tahira and Geiger, Mackenzie and Khan, Saad A.}, year={2021}, month={Aug}, pages={479–492} } @article{ramesh_davis_roros_eiben_fabiani_smith_reynolds_pourdeyhimi_khan_genzer_et al._2021, title={Dual-Responsive Microgels for Structural Repair and Recovery of Nonwoven Membranes for Liquid Filtration}, volume={3}, ISSN={["2637-6105"]}, url={https://doi.org/10.1021/acsapm.0c01360}, DOI={10.1021/acsapm.0c01360}, abstractNote={This study presents dual-responsive colloidal microgels to repair nonwoven fiber mats (NWFs) and recover their native morphological and functional properties. The formulation comprises poly(N-isopr...}, number={3}, journal={ACS APPLIED POLYMER MATERIALS}, publisher={American Chemical Society (ACS)}, author={Ramesh, Srivatsan and Davis, Jack and Roros, Alexandra and Eiben, Justin and Fabiani, Thomas and Smith, Ryan and Reynolds, Lewis and Pourdeyhimi, Behnam and Khan, Saad and Genzer, Jan and et al.}, year={2021}, month={Mar}, pages={1508–1517} } @article{barilovits_khan_shim_2021, title={Experimental Investigation of the Fiber Formation Process and Web Structures Using an Annular Meltblowing Spinneret}, volume={60}, ISSN={["0888-5885"]}, url={https://doi.org/10.1021/acs.iecr.1c01080}, DOI={10.1021/acs.iecr.1c01080}, abstractNote={This research experimentally investigates the fiber and web formation process of an array of annular meltblown spinnerets. In this design, the molten polymer is extruded from an array of outlets, each of which is individually surrounded by a concentric high-velocity heated air stream. With its multirow capability, it potentially becomes a high-productivity microfiber fabrication process. We experimentally investigate the effects of critical processing parameters and material properties on the fiber and web formation process. First, the polymer thermal and rheological behavior is presented. Next, a detailed three-dimensional air temperature and velocity profile, measured in the absence of spinning fibers, is presented for an array of supplied temperatures and internal machine air pressures. Web analysis in relation to this air profile shows that smaller fibers in cooler air streams require shorter die-collector distances to form bonded fabrics. Calculations are then made that show polymer spinning temperature is largely determined by air temperature, a distinguishing feature of this meltblowing design. Finally, a full factorial variation of air temperature, air speed, and polymer throughput is shown that relates processing conditions to fiber diameter distribution. Median diameters are well described by an empirical model and ranged from less than 1 μm to almost 14 μm.}, number={37}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, publisher={American Chemical Society (ACS)}, author={Barilovits, Stephen and Khan, Saad A. and Shim, Eunkyoung}, year={2021}, month={Sep}, pages={13627–13636} } @article{dufficy_corder_dennis_fedkiw_khan_2021, title={Guar Gel Binders for Silicon Nanoparticle Anodes: Relating Binder Rheology to Electrode Performance}, volume={13}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.1c10776}, DOI={10.1021/acsami.1c10776}, abstractNote={Binding agents are a critical component of Si-based anodes for lithium-ion batteries. Herein, we introduce a composite hydrogel binder consisting of carbon black (CB) and guar, which is chemically cross-linked with glutaraldehyde as a means to reinforce the electrode structure during lithiation and improve electronic conductivity. Dynamic rheological measurements are used to monitor the cross-linking reaction and show that rheology plays a significant role in binder performance. The cross-linking reaction occurs at a faster rate and produces stronger networks in the presence of CB, as evidenced from higher gel elastic modulus in guar + CB gels than guar gels alone. Silicon nanoparticle (SiNP) electrodes that use binders with low cross-link densities (trxn < 2 days) demonstrate discharge capacities ∼1200 mAh g-1 and Coulombic efficiencies >99.8% after 300 cycles at 1-C rate. Low cross-link densities likely increase the capacity of SiNP anodes because of binder-Si hydrogen-bonding interactions that accommodate volume expansions. In addition, the cross-linked binder demonstrates the potential for self-healing, as evidenced by an increased elastic modulus after the gel was mechanically fragmented, which may preserve the electrode microstructure during lithiation and increase capacity retention. The composite hydrogel with integrated conductive additives gives promise to a new type of binder for next-generation lithium-ion batteries.}, number={43}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Dufficy, Martin K. and Corder, Ria D. and Dennis, Kimberly A. and Fedkiw, Peter S. and Khan, Saad A.}, year={2021}, month={Nov}, pages={51403–51413} } @article{adhikari_jani_hsiao_rojas_khan_2021, title={Interfacial Contributions in Nanodiamond-Reinforced Polymeric Fibers}, volume={125}, ISSN={["1520-5207"]}, url={https://doi.org/10.1021/acs.jpcb.1c03361}, DOI={10.1021/acs.jpcb.1c03361}, abstractNote={We study the interfacial energy parameters that explain the reinforcement of polymers with nanodiamond (ND) and the development of mechanical strength of electrospun ND-reinforced composites. Thermodynamic parameters such as the wettability ratio, work of spreading and dispersion/aggregation transition are used to derive a criterion to predict the dispersibility of carboxylated ND (cND) in polymeric matrices. Such a criterion for dispersion (Dc) is applied to electrospun cND-containing poly(vinyl alcohol) (PVA), polyacrylonitrile (PAN), and polystyrene (PS) fiber composites. The shifts in glass transition temperature (ΔTg), used as a measure of polymer/cND interfacial interactions and hence the reinforcement capability of cNDs, reveal a direct correlation with the thermodynamic parameter Dc in the order of PAN < PS < PVA. Contrary to expectation, however, the tensile strength of the electrospun fibers correlates with the Dc and ΔTg only for semicrystalline polymers (PAN < PVA) while the amorphous PS displays a maximum reinforcement with cND. Such conflicting results reveal a synergy that is not captured by thermodynamic considerations alone but also factor in the contributions of polymer/cND interface stress transfer efficiency. Our findings open the possibility for tailoring the interfacial interactions in polymer-ND fiber composites to achieve maximum mechanical reinforcement.}, number={36}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, publisher={American Chemical Society (ACS)}, author={Adhikari, Prajesh and Jani, Pallav K. and Hsiao, Lilian C. and Rojas, Orlando J. and Khan, Saad A.}, year={2021}, month={Sep}, pages={10312–10323} } @article{farias_haeri_khan_2021, title={Linking polymer hydrophobicity and molecular interactions to rheology and tribology in phospholipid-containing complex gels}, volume={584}, ISSN={["1095-7103"]}, DOI={10.1016/j.jcis.2020.09.113}, abstractNote={The rheological behavior and frictional properties (macroscopic level) of systems containing a hydrophobically modified polymer and phospholipids depend on the hydrophobic association that occur between the hydrophobic moiety of the polymer and the phospholipid tails (molecular level). The hydrophobicity of the polymer can thus be used to control its interactions with phospholipids, and manipulate complex gel macroscopic behavior. By using systems composed of a crosslinked hydrophobically modified polyacrylic acid (HMPAA) or a crosslinked polyacrylic acid polymer (PAA) and phospholipids, we examine the underlying mechanisms through which the components interact using isothermal titration calorimetry (ITC) and their effect on rheological and tribological characteristics of complex gels. We find the systems containing HMPAA and phospholipid exhibit gel-like behavior with the elastic modulus increasing substantially upon phospholipid addition due to hydrophobic interactions that result in a more interconnected network formation, as evidenced by ITC measurements. Similar experiments with a crosslinked polyacrylic acid polymer (PAA) show no interactions, lending credence to our hypothesis. In addition, soft tribological behavior shows lower friction coefficients at low entrainment speeds with HMPAA concentration and the addition of phospholipid, while no change in friction coefficient was observed in the case of increasing PAA concentration, indicating HMPAA and phospholipids to be interacting with the soft PDMS contacts.}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, author={Farias, Barbara V. and Haeri, Farrah and Khan, Saad A.}, year={2021}, month={Feb}, pages={134–144} } @article{jin_facchine_khan_rojas_spontak_2021, title={Mesophase characteristics of cellulose nanocrystal films prepared from electrolyte suspensions}, volume={599}, ISSN={["1095-7103"]}, url={https://doi.org/10.1016/j.jcis.2021.04.071}, DOI={10.1016/j.jcis.2021.04.071}, abstractNote={Cellulose nanocrystals (CNCs) exhibit a cholesteric mesophase above a critical concentration in aqueous suspensions. Above this concentration, CNCs self-organize into left-handed helicoidal structures that can be preserved in dried, stratified films. In this systematic study, we have prepared optically-active CNC films cast from different electrolyte suspensions and investigated, via circular dichroism and other techniques, the effects of counterion type (six mono/divalent salts, including those responsible for promoting "salting-out" and "salting-in" in the Hofmeister series) and ionic strength on mesomorphic behavior and cholesteric arrangement. The presence of electrolytes influences CNC colloidal stability by compressing the electric double layer and altering interactions among neighboring CNCs and water, thereby affecting the extent to which the CNCs form a mesophase. Interestingly, mesomorphic behavior and CNC alignment appear to be sensitive to cationic radius and charge valence, in which case the optical properties of CNC films can be adjusted for targeted sustainable applications. Such heuristic rules can be valuable for predicting the stability and characteristics of CNC microstructure in designer coatings and thin films prepared by introducing suitable cations prior to film formation.}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, publisher={Elsevier BV}, author={Jin, Soo-Ah and Facchine, Emily G. and Khan, Saad A. and Rojas, Orlando J. and Spontak, Richard J.}, year={2021}, month={Oct}, pages={207–218} } @article{farias_khan_2021, title={Probing gels and emulsions using large-amplitude oscillatory shear and frictional studies with soft substrate skin surrogates}, volume={201}, ISSN={["1873-4367"]}, url={https://doi.org/10.1016/j.colsurfb.2021.111595}, DOI={10.1016/j.colsurfb.2021.111595}, abstractNote={Water swellable crosslinked polymers are widely used in oil-in-water emulsions for the healthcare and cosmetic industries due to their thickening properties. In this study, we investigate the rheological and lubrication behavior of a microgel-forming polymer, a lightly-crosslinked hydrophobically modified polyacrylic acid (HMPAA), in an aqueous medium and in an emulsion. Hydrogenated phosphatidylcholine, a class of phospholipids, is used as a surfactant in the emulsions composed of different oil content. Rheological behavior is probed both in the linear and non-linear regimes using small strain amplitude and large amplitude oscillatory shear (LAOS) experiments, respectively. We observe all systems to exhibit gel-like behavior with the elastic modulus (G’) dominating and being frequency independent. Lissajous-Bowditch plots and nonlinear parameters obtained under large deformation show that the emulsions can resist greater deformations with smaller increase in the viscous dissipation when compared to a HMPAA gel. For tribology experiments, friction curves in a range of entrainment speeds are examined using substrates to mimic the skin surface (PDMS and Bioskin®). The role of polymer hydrophobicity on the different substrates are also explored by comparing the behavior of HMPAA to that of its hydrophilic analog, a polyacrylic acid highly crosslinked. We find the friction coefficient to be dependent on the hydrophobicity of the substrate and the polymer as well as the substrate roughness. These results taken together provide insights in the formulation of skincare products with efficient lubrication properties for different skin characteristics.}, journal={COLLOIDS AND SURFACES B-BIOINTERFACES}, publisher={Elsevier BV}, author={Farias, Barbara V and Khan, Saad A.}, year={2021}, month={May} } @article{cutright_harris_ramesh_khan_genzer_menegatti_2021, title={Surface-Bound Microgels for Separation, Sensing, and Biomedical Applications}, volume={31}, ISSN={["1616-3028"]}, url={https://doi.org/10.1002/adfm.202104164}, DOI={10.1002/adfm.202104164}, abstractNote={Abstract}, number={47}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley}, author={Cutright, Camden C. and Harris, Jacob L. and Ramesh, Srivatsan and Khan, Saad A. and Genzer, Jan and Menegatti, Stefano}, year={2021}, month={Aug} } @article{pirzada_sohail_tripathi_farias_mathew_li_opperman_khan_2021, title={Toward Sustainable Crop Protection: Aqueous Dispersions of Biodegradable Particles with Tunable Release and Rainfastness}, volume={11}, ISSN={["1616-3028"]}, url={https://doi.org/10.1002/adfm.202108046}, DOI={10.1002/adfm.202108046}, abstractNote={Abstract}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley}, author={Pirzada, Tahira and Sohail, Mariam and Tripathi, Anurodh and Farias, Barbara V and Mathew, Reny and Li, Chunying and Opperman, Charles H. and Khan, Saad A.}, year={2021}, month={Nov} } @article{corder_gadi_vachieri_jayes_cullen_khan_taylor_2021, title={Using rheology to quantify the effects of localized collagenase treatments on uterine fibroid digestion}, volume={134}, ISSN={["1878-7568"]}, DOI={10.1016/j.actbio.2021.08.003}, abstractNote={Uterine fibroids are stiff, benign tumors containing excessive, disordered collagens that occur in 70-80% of women before age 50 and cause bleeding and pain. Collagenase Clostridium histolyticum (CCH) is a bacterial enzyme capable of digesting the collagens present in fibroids. By combining CCH with injectable drug delivery systems to enhance effectiveness, a new class of treatments could be developed to reduce the stiffness of fibroids, preventing the need for surgical removal and preserving fertility. In this work, we achieved localization of CCH via physical entrapment by co-injecting a thermoresponsive pNIPAM-based polymeric delivery system called LiquoGel (LQG), which undergoes a sol-gel transition upon heating. Toxicity study results for LQG injected subcutaneously into mice demonstrate that LQG does not induce lesions or other adverse effects. We then used rheology to quantify the effects of localized CCH injections on the modulus and viscoelasticity of uterine fibroids, which exhibit gel-like behavior, through ex vivo and in vivo digestion studies. Ex vivo CCH injections reduce the tissue modulus by over two orders of magnitude and co-injection of LQG enhances this effect. Rheological results from an in vivo digestion study in mice show a significant reduction in tissue modulus and increase in tissue viscoelasticity 7 days after a single injection of LQG+CCH. Parallel histological staining validates that the observed rheological changes correspond to an increase in collagen lysis after treatment by LQG+CCH. These results show promise for development of injectable and localized enzymatic therapies for uterine fibroids and other dense tumors. STATEMENT OF SIGNIFICANCE: Uterine fibroids are stiff, benign tumors containing high collagen levels that cause bleeding and pain in women. Fertility-preserving and minimally-invasive treatments to soften fibroids are needed as an alternative to surgical removal via hysterectomy. We demonstrate through ex vivo and in vivo studies that co-injecting a thermoresponsive polymer delivery system (LQG) alongside a bacterial collagenase (CCH) enzyme significantly increases treatment effectiveness at softening fibroids through CCH localization. We use rheology to measure the modulus and viscoelasticity of fibroids and histology to show that fibroid softening corresponds to a decrease in collagen after treatment with LQG+CCH. These results highlight the utility of rheology at quantifying tissue properties and present a promising injectable therapy for fibroids and other dense tumors.}, journal={ACTA BIOMATERIALIA}, author={Corder, Ria D. and Gadi, Sashi V and Vachieri, Robert B. and Jayes, Friederike L. and Cullen, John M. and Khan, Saad A. and Taylor, Darlene K.}, year={2021}, month={Oct}, pages={443–452} } @article{pirzada_ashrafi_xie_khan_2020, title={Cellulose Silica Hybrid Nanofiber Aerogels: From Sol–Gel Electrospun Nanofibers to Multifunctional Aerogels}, url={https://doi.org/10.1002/adfm.201907359}, DOI={10.1002/adfm.201907359}, abstractNote={Abstract}, journal={Advanced Functional Materials}, author={Pirzada, Tahira and Ashrafi, Zahra and Xie, Wenyi and Khan, Saad A.}, year={2020}, month={Jan} } @article{corder_adhikari_burroughs_rojas_khan_2020, title={Cellulose nanocrystals for gelation and percolation-induced reinforcement of a photocurable poly(vinyl alcohol) derivative}, volume={16}, url={https://doi.org/10.1039/D0SM01376E}, DOI={10.1039/D0SM01376E}, abstractNote={We examine how cellulose nanocrystals affect the rheology of a photoactive poly(vinyl alcohol) derivative before, during, and after photocrosslinking.}, number={37}, journal={Soft Matter}, publisher={Royal Society of Chemistry (RSC)}, author={Corder, Ria D. and Adhikari, Prajesh and Burroughs, Michael C. and Rojas, Orlando J. and Khan, Saad A.}, year={2020}, pages={8602–8611} } @article{wang_shi_tripathi_chakraborty_parsons_khan_2020, title={Designing Intrinsically Microporous Polymer (PIM-1) Microfibers with Tunable Morphology and Porosity via Controlling Solvent/Nonsolvent/Polymer Interactions}, volume={2}, url={https://doi.org/10.1021/acsapm.0c00386}, DOI={10.1021/acsapm.0c00386}, abstractNote={In this study, we present the fabrication of fibers with tunable morphology and porosity from an intrinsically microporous polymer, PIM-1, using a simple one-step electrospinning technique. The met...}, number={6}, journal={ACS Applied Polymer Materials}, publisher={American Chemical Society (ACS)}, author={Wang, Siyao and Shi, Kaihang and Tripathi, Anurodh and Chakraborty, Ushno and Parsons, Gregory N. and Khan, Saad A.}, year={2020}, month={Jun}, pages={2434–2443} } @article{smith_fabiani_wang_ramesh_khan_santiso_silva_gorman_menegatti_2020, title={Exploring the physicochemical and morphological properties of peptide‐hybridized dendrimers ( DendriPeps ) and their aggregates}, volume={58}, ISSN={2642-4150 2642-4169}, url={http://dx.doi.org/10.1002/pol.20200277}, DOI={10.1002/pol.20200277}, abstractNote={Abstract}, number={16}, journal={Journal of Polymer Science}, publisher={Wiley}, author={Smith, Ryan J. and Fabiani, Thomas and Wang, Siyao and Ramesh, Srivatsan and Khan, Saad and Santiso, Erik and Silva, Fernando Luis Barroso and Gorman, Christopher and Menegatti, Stefano}, year={2020}, month={Jul}, pages={2234–2247} } @article{lavoie_rojas_khan_shim_2020, title={Migration Effects of Fluorochemical Melt Additives for Alcohol Repellency in Polypropylene Nonwoven Materials}, volume={12}, url={https://doi.org/10.1021/acsami.0c10144}, DOI={10.1021/acsami.0c10144}, abstractNote={The use of bulk polymer melt additives provides a facile, industrially relevant approach to tailor properties of polymer surfaces for many different applications. These melt additives, when blended with polymers prior to melt spinning, migrate to the fiber surface and influence surface functionality. While the use of bulk polymer melt additives to impart hydrophilicity or oleophobicity is well studied, the impact of the fiber formation process on additive migration and resultant repellency of nonwoven media products remains largely unexplored. In this study, we produce fluorochemical melt additive containing meltblown nonwovens, and establish methods for characterization of fiber mat surface composition and repellency. Repellency of low surface tension fluids is a significant challenge, and is of particular importance in the creation of medical garments such as surgical gowns and masks which must perform as liquid barriers even when exposed to alcohol based solutions. Similarly, melt additives are also used in the production of electret air filtration devices. Electret filters are imbued with charges in order to enhance particle capture performance, but this charge can be negated through wetting by low surface tension fluids. To address this challenge, the changing composition of fiber surfaces due to the migration of additives is monitored via X-ray Photoelectron Spectroscopy (XPS), then related to repellency of alcohol solutions by contact angle analysis. We demonstrate that for the samples tested a fluorine to carbon (F/C) ratio of 0.35 is sufficient to prevent wicking of isopropanol droplets, and higher surface tension fluids could be repelled by fiber mats with lower fluorine content. Through the use of cross-sectional ToF-SIMS analysis, we find that migration of additives is key to the performance of samples with low additive loadings, and that these phenomena are heavily influenced by many nonwoven manufacturing parameters including fiber size, die-to-collector distance, and polymer resin melt flow rates.}, number={32}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Lavoie, Joseph H. and Rojas, Orlando J. and Khan, Saad A. and Shim, Eunkyoung}, year={2020}, month={Aug}, pages={36787–36798} } @article{pervaje_tilly_detwiler_spontak_khan_santiso_2020, title={Molecular Simulations of Thermoset Polymers Implementing Theoretical Kinetics with Top-Down Coarse-Grained Models}, volume={53}, url={https://doi.org/10.1021/acs.macromol.9b02255}, DOI={10.1021/acs.macromol.9b02255}, abstractNote={Thermoset polymers are examples of chemically cured, network-forming materials whose bulk properties depend sensitively on formulation chemistry and reaction conditions. In this work, we employ mol...}, number={7}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Pervaje, Amulya K. and Tilly, Joseph C. and Detwiler, Andrew T. and Spontak, Richard J. and Khan, Saad A. and Santiso, Erik E.}, year={2020}, month={Apr}, pages={2310–2322} } @article{farias_brown_hearn_nunn_shenderova_khan_2020, title={Nanodiamond-stabilized Pickering emulsions: Microstructure and rheology}, volume={580}, ISSN={["1095-7103"]}, DOI={10.1016/j.jcis.2020.07.030}, abstractNote={We envisage the use of hydroxylated detonation nanodiamonds (ND-OH), a relatively novel carbonaceous filler with high adsorption activity, small size, and large surface area to create Pickering emulsions. The emulsion behavior under shear and the extent to which the microstructure can rebuild after breakdown is dependent on its yield stress. Using a model system consisting of isopropyl palmitate and water stabilized by ND-OH particles, we investigate the stability of these emulsions, their microstructure and rheological behavior as a function of ND-OH concentration. Confocal microscopy reveals that increasing ND-OH concentration results in smaller droplet sizes in the emulsions. This behavior is consistent with our rheological results of higher elastic modulus G′ and yield stress of the emulsion with increased ND-OH, as the presence of smaller droplets facilitates the formation of a densely packed network. We find the rheological behavior of these emulsions to be a hybrid of colloidal gels and surfactant-stabilized emulsions, with interparticle interactions and droplets deformability dictating their elasticity and yield stress behavior. Structure recovery following large shear reveals the degree of microstructure recovery to depend on the applied stress, with the recovered modulus collapsing into a single master-curve when the applied stress is scaled by the yield stress.}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, author={Farias, Barbara V and Brown, Derek and Hearn, Allison and Nunn, Nicholas and Shenderova, Olga and Khan, Saad A.}, year={2020}, month={Nov}, pages={180–191} } @article{cutright_finkelstein_orlowski_mcintosh_brotherton_fabiani_khan_genzer_menegatti_2020, title={Nonwoven fiber mats with thermo-responsive permeability to inorganic and organic electrolytes}, volume={616}, ISSN={["1873-3123"]}, DOI={10.1016/j.memsci.2020.118439}, abstractNote={This study presents the development and characterization of nonwoven fiber mats (NWFs) with stimuli-controlled permeability. An ensemble of membranes was initially constructed by coating the fibers of polypropylene NWFs with a layer of poly ((N-isopropyl acrylamide)-co-(acrylic acid)) (PNIPAm-co-AA) hydrogel. Different coatings were produced by varying the PNIPAm/AA monomer ratio between 3.9 and 18.6. The thermo-responsive layer is expanded at room temperature and contracts when heated above its lower critical solution temperature (LCST). The resulting membranes were first characterized via laser scanning microscopy and fluorescence confocal microscopy to evaluate the thickness and morphology of the hydrogel layer. Microscopy shows uniform coating of the fibers, with a thickness comparable to the fiber diameter, and homogeneous filling of the pore space. The permeability of the NWFs was then evaluated using different solutes, namely an inorganic salt (sodium chloride), an organic acid (citric acid), and an amphiphilic drug (Doxorubicin). These tests consistently show that the flux of the solute is (1) higher at temperatures > LCST, where the hydrogel layer collapses and opens the pore space, and (2) decreases at room temperature (80:20), and less toxic alternative to Triton X-100 surfactant. Finally, alginate-only nanofibers that are also water-insoluble are obtained by crosslinking the electrospun fibers with calcium and subsequently removing the PEO and surfactants by soaking the nanofibers in water.}, number={1}, journal={Carbohydrate Polymers}, publisher={Elsevier BV}, author={Bonino, Christopher A. and Krebs, Melissa D. and Saquing, Carl D. and Jeong, Sung In and Shearer, Kimberly L. and Alsberg, Eben and Khan, Saad A.}, year={2011}, month={Apr}, pages={111–119} } @article{bonino_ji_lin_toprakci_zhang_khan_2011, title={Electrospun Carbon-Tin Oxide Composite Nanofibers for Use as Lithium Ion Battery Anodes}, volume={3}, ISSN={["1944-8252"]}, url={https://publons.com/publon/674395/}, DOI={10.1021/am2004015}, abstractNote={Composite carbon-tin oxide (C-SnO(2)) nanofibers are prepared by two methods and evaluated as anodes in lithium-ion battery half cells. Such an approach complements the long cycle life of carbon with the high lithium storage capacity of tin oxide. In addition, the high surface-to-volume ratio of the nanofibers improves the accessibility for lithium intercalation as compared to graphite-based anodes, while eliminating the need for binders or conductive additives. The composite nanofibrous anodes have first discharge capacities of 788 mAh g(-1) at 50 mA g(-1) current density, which are greater than pure carbon nanofiber anodes, as well as the theoretical capacity of graphite (372 mAh g(-1)), the traditional anode material. In the first protocol to fabricate the C-SnO(2) composites, tin sulfate is directly incorporated within polyacrylonitrile (PAN) nanofibers by electrospinning. During a thermal treatment the tin salt is converted to tin oxide and the polymer is carbonized, yielding carbon-SnO(2) nanofibers. In the second approach, we soak the nanofiber mats in tin sulfate solutions prior to the final thermal treatment, thereby loading the outer surfaces with SnO(2) nanoparticles and raising the tin content from 1.9 to 8.6 wt %. Energy-dispersive spectroscopy and X-ray diffraction analyses confirm the formation of conversion of tin sulfate to tin oxide. Furthermore, analysis with Raman spectroscopy reveals that the additional salt soak treatment from the second fabrication approach increases in the disorder of the carbon structure, as compared to the first approach. We also discuss the performance of our C-SnO(2) compared with its theoretical capacity and other nanofiber electrode composites previously reported in the literature.}, number={7}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Bonino, Christopher A. and Ji, Liwen and Lin, Zhan and Toprakci, Ozan and Zhang, Xiangwu and Khan, Saad A.}, year={2011}, month={Jul}, pages={2534–2542} } @article{canbolat_tang_bernacki_pourdeyhimi_khan_2011, title={Mammalian Cell Viability in Electrospun Composite Nanofiber Structures}, volume={11}, ISSN={["1616-5195"]}, DOI={10.1002/mabi.201100108}, abstractNote={Abstract}, number={10}, journal={MACROMOLECULAR BIOSCIENCE}, author={Canbolat, Mehmet Fatih and Tang, Christina and Bernacki, Susan H. and Pourdeyhimi, Behnam and Khan, Saad}, year={2011}, month={Oct}, pages={1346–1356} } @article{bonino_samorezov_jeon_alsberg_khan_2011, title={Real-time in situ rheology of alginate hydrogel photocrosslinking}, volume={7}, ISSN={1744-683X 1744-6848}, url={http://dx.doi.org/10.1039/c1sm06109g}, DOI={10.1039/c1sm06109g}, abstractNote={The reaction dynamics of biodegradable, photocrosslinkable sodium alginate hydrogels are studied by in situ, dynamic rheology. Alginate, chemically-modified with methacrylate groups, crosslinks by ultraviolet (UV) light exposure in the presence of a photoinitiator. The gel formation is monitored during UV irradiation from a light emitting diode (LED) bottom plate fixture on the rheometer. Material properties of the hydrogels, including gel points and relaxation exponent, are evaluated using the Winter-Chambon criteria. We also report a new, complementary empirical method for determining the gel point from the reduction in sample strain at the onset of gelation, via monitoring the strain curve. In addition, the crosslinking dynamics and hydrogel moduli are altered by changing the UV irradiation intensities (3–15 mW cm−2) and degree of methacrylation (5–25%). Dynamic rheological measurements of hydrogels as described in this paper are a potentially powerful tool to elucidate the dynamics of gelation and predict mechanical properties. This technique may aid in the design of polymer formulations with light-reactive chemical species, which have tunable properties that can be matched to a range of applications, including regenerative medicine.}, number={24}, journal={Soft Matter}, publisher={Royal Society of Chemistry (RSC)}, author={Bonino, Christopher A. and Samorezov, Julia E. and Jeon, Oju and Alsberg, Eben and Khan, Saad A.}, year={2011}, pages={11510–11517} } @article{krishnan_seifert_lee_khan_spontak_2010, title={Cosolvent-regulated time-composition rheological equivalence in block copolymer solutions}, volume={6}, ISSN={["1744-6848"]}, DOI={10.1039/c0sm00573h}, abstractNote={The morphological and mechanical attributes of triblock copolymer solutions composed of miscible, midblock-selective solvents are investigated by small-angle scattering and dynamic rheology. Variation in cosolvent composition at constant copolymer concentration has little effect on copolymer morphology, but promotes large differences in matrix relaxation, as evinced by changes in the shape of isothermal frequency spectra. Shifting these spectra in the frequency domain reveals the existence of time–composition equivalence, wherein shift factors scale with the viscosity of the cosolvent mixture.}, number={18}, journal={SOFT MATTER}, author={Krishnan, Arjun S. and Seifert, Soenke and Lee, Byeongdu and Khan, Saad A. and Spontak, Richard J.}, year={2010}, pages={4331–4334} } @article{jeong_krebs_bonino_khan_alsberg_2010, title={Electrospun Alginate Nanofibers with Controlled Cell Adhesion for Tissue Engineeringa}, volume={10}, ISSN={1616-5187}, url={http://dx.doi.org/10.1002/mabi.201000046}, DOI={10.1002/mabi.201000046}, abstractNote={Abstract}, number={8}, journal={Macromolecular Bioscience}, publisher={Wiley}, author={Jeong, Sung In and Krebs, Melissa D. and Bonino, Christopher A. and Khan, Saad A. and Alsberg, Eben}, year={2010}, month={Jun}, pages={934–943} } @article{talwar_krishnan_hinestroza_pourdeyhimi_khan_2010, title={Electrospun Nanofibers with Associative Polymer-Surfactant Systems}, volume={43}, ISSN={["1520-5835"]}, DOI={10.1021/ma1013447}, abstractNote={Associative polymers are unique in their structure with pendant hydrophobes attached to their hydrophilic backbone, enabling associations between the hydrophobes and forming junctions in aqueous solutions. In this study, we examine efforts to produce electrospun nanofibers of associative polymers in conjunction with a readily spinnable polymer. Scanning electron micrograph (SEM) images reveal that the solution rheology sets an upper limit to the concentration of associative polymer that can be successfully electrospun. However, addition of nonionic surfactants to the precursor solution results in significant improvement in nanofiber morphology as evinced from reduced beading. Through judicious use of nonionic surfactants to modulate solution viscoelastic properties, we are able to obtain defect-free nanofiber morphology and gain new insights into the fundamentals of the electrospinning process. In particular, we find that solution viscoelasticity as measured in terms of the relaxation time, rather than viscosity as typically hypothesized, controls the nanofiber formation process.}, number={18}, journal={MACROMOLECULES}, author={Talwar, Sachin and Krishnan, Arjun S. and Hinestroza, Juan P. and Pourdeyhimi, Behnam and Khan, Saad A.}, year={2010}, month={Sep}, pages={7650–7656} } @article{tang_saquing_harding_khan_2010, title={In Situ Cross-Linking of Electrospun Poly(vinyl alcohol) Nanofibers}, volume={43}, ISSN={["1520-5835"]}, DOI={10.1021/ma902269p}, abstractNote={We examine single step reactive electrospinning of poly(vinyl alcohol) (PVA) and a chemical cross-linking agent, glutaraldehyde (GA), with hydrochloric acid (HCl) as a catalyst to generate water insoluble PVA nanofibers. Such an approach using a conventional setup with no modification enables the fibers to cross-link during the electrospinning process, thereby eliminating the need for post-treatment. Significant changes in the rheological properties occur during in situ cross-linking, which we correlate with electrospinnability. In particular, we associate changes in dynamic rheological properties to changes in fiber morphology for two regions: (1) below the critical concentration to electrospin PVA only and (2) above the critical concentration to electrospin PVA only. In region 1 fiber morphology changes from beaded fibers to uniform fibers to flat fibers, and in region 2 fiber morphology changes from uniform fibers to flat fibers. Electrospinning windows to generate uniform fibers for both regions are d...}, number={2}, journal={MACROMOLECULES}, author={Tang, Christina and Saquing, Carl D. and Harding, Jonathon R. and Khan, Saad A.}, year={2010}, month={Jan}, pages={630–637} } @article{mahammad_abdala_roberts_khan_2010, title={Manipulation of hydrophobic interactions in associative polymers using cyclodextrin and enzyme}, volume={6}, ISSN={1744-683X 1744-6848}, url={http://dx.doi.org/10.1039/c0sm00054j}, DOI={10.1039/c0sm00054j}, abstractNote={We examine a new approach to reversibly modulate hydrophobic interactions in associative polymers using cyclodextrins (CD) and enzymes that cause scission of the α-1, 4 linkages in cyclodextrins. The associative polymers have a comb-like structure with pendant hydrophobic groups randomly attached to the polymer backbone. The intermolecular interaction between hydrophobic groups forms a transient network resulting in thickening of solutions containing the polymer. The CDs, doughnut-shaped cyclic polysaccharides, encapsulate the hydrophobes within their hydrophobic cavity and eliminate hydrophobic interactions. This results in several orders of magnitude reduction in solution viscosity and other viscoelastic properties. Subsequent degradation of the CDs by enzymes restores the hydrophobic interactions and the original rheological properties. A rheokinetic model is developed to describe the kinetics of the enzymatic reactions. The model accounts for equilibrium between the CD bound to the hydrophobes and free CD in solution and assumes the enzyme hydrolyzes only the free CD in the solution, which causes the release of the bound CDs in order to maintain equilibrium. The reaction is assumed to follow Michaelis Menten kinetics and the kinetic parameters are determined by tracking the changes in the viscoelastic properties of the polymer solution during the enzymatic scission of CD. The effects of enzyme concentration, polymer concentration and temperature on the rate of recovery of the original rheological properties are experimentally determined, and used to validate the trends of the rheokinetic model.}, number={17}, journal={Soft Matter}, publisher={Royal Society of Chemistry (RSC)}, author={Mahammad, Shamsheer and Abdala, Ahmed and Roberts, George W. and Khan, Saad A.}, year={2010}, pages={4237–4245} } @article{arvidson_khan_gorga_2010, title={Mesomorphic-alpha-Monoclinic Phase Transition in Isotactic Polypropylene: A Study of Processing Effects on Structure and Mechanical Properties}, volume={43}, ISSN={["1520-5835"]}, DOI={10.1021/ma1001645}, abstractNote={We report the enthalpy for the mesomorphic to α-monoclinic phase transition in polypropylene under varying thermal treatments. The mesomorphic phase is created by fiber spinning and rapid quenching methods and identified using wide-angle X-ray diffraction and differential scanning calorimetry. Fiber mesomorphs are found to have a 3-fold increase in enthalpy of transition per gram of mesophase compared with our measurements of quenched polypropylene and previous reports of quenched polypropylene. In addition, systematic tensile testing over a range of spin speeds and polymer morphologies reveals that the presence of mesomorphic regions does not correlate with reduced fiber strength as has been previously suggested. Fiber true stress−true strain curves obtained at varying take-up velocities are compared to determine the “tensile strain shift”, which should theoretically provide a measure of molecular orientation. We find that the tensile strain shift correlates with birefringence, thereby providing an alter...}, number={6}, journal={MACROMOLECULES}, author={Arvidson, Sara A. and Khan, Saad A. and Gorga, Russell E.}, year={2010}, month={Mar}, pages={2916–2924} } @misc{desimone_siripurapu_khan_spontak_royer_2010, title={Nano-and micro-cellular foamed thin-walled material, and processes and apparatuses for making the same}, volume={7,658,989}, number={2010 Feb. 9}, author={DeSimone, J. M. and Siripurapu, S. and Khan, S. A. and Spontak, R. J. and Royer, J.}, year={2010} } @article{gaines_smith_samseth_khan_spontak_2010, title={Nanoparticle Network Formation in Nanostructured and Disordered Block Copolymer Matrices}, volume={5}, ISSN={["1556-276X"]}, DOI={10.1007/s11671-010-9775-y}, abstractNote={Incorporation of nanoparticles composed of surface-functionalized fumed silica (FS) or native colloidal silica (CS) into a nanostructured block copolymer yields hybrid nanocomposites whose mechanical properties can be tuned by nanoparticle concentration and surface chemistry. In this work, dynamic rheology is used to probe the frequency and thermal responses of nanocomposites composed of a symmetric poly(styrene-b-methyl methacrylate) (SM) diblock copolymer and varying in nanoparticle concentration and surface functionality. At sufficiently high loading levels, FS nanoparticle aggregates establish a load-bearing colloidal network within the copolymer matrix. Transmission electron microscopy images reveal the morphological characteristics of the nanocomposites under these conditions.}, number={10}, journal={NANOSCALE RESEARCH LETTERS}, author={Gaines, Michelle K. and Smith, Steven D. and Samseth, Jon and Khan, Saad A. and Spontak, Richard J.}, year={2010}, month={Oct}, pages={1712–1718} } @article{appaw_gilbert_khan_kadla_2010, title={Phase separation and heat-induced gelation characteristics of cellulose acetate in a mixed solvent system}, volume={17}, ISSN={0969-0239 1572-882X}, url={http://dx.doi.org/10.1007/s10570-010-9406-x}, DOI={10.1007/s10570-010-9406-x}, number={3}, journal={Cellulose}, publisher={Springer Science and Business Media LLC}, author={Appaw, Collins and Gilbert, Richard D. and Khan, Saad A. and Kadla, John F.}, year={2010}, month={Mar}, pages={533–538} } @article{spagnola_gong_arvidson_jur_khan_parsons_2010, title={Surface and sub-surface reactions during low temperature aluminium oxide atomic layer deposition on fiber-forming polymers}, volume={20}, ISSN={["0959-9428"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000277563800026&KeyUID=WOS:000277563800026}, DOI={10.1039/c0jm00355g}, abstractNote={Fundamental reaction processes between vapor-phase chemical precursors and high molecular weight polymers are important for polymer coating, encapsulation and surface modification. Using trimethylaluminium and water in an atomic layer deposition (ALD) exposure sequence, reactions between vapor-phase trimethylaluminium and common polymers with different substituents are quantified using in situ infrared transmission analysis. Exposing polypropylene to trimethylaluminium results in reactant uptake with minimal precursor/polymer reaction, but the precursor/water ALD sequence leads to subsurface alumina nucleation. A similar treatment to polyvinyl alcohol and polyamide-6 results in rapid precursor diffusion and significant reaction observed by IR, and the extent of reaction is consistent with results from in situ quartz crystal microgravimetry and transmission electron microscopy. Reacting trimethylaluminium with polyamide-6 leads to methyl group insertion into the amide carbonyl group and interaction with the hydrogen-bonded amine units. Multiple ALD reaction cycles produce film coatings on all polymers studied, but the coating structure depends strongly on the starting polymer composition. For the weakly interacting polypropylene, cross-sectional transmission electron microscopy demonstrates enhanced sub-surface growth at 90 °C as compared to that at 60 °C, while images of coated polyamide-6 fibers showed that growth is not strongly temperature dependent in that range. Micrograph images of polyamide-6 samples exposed to extended TMA doses revealed significant modification of the fiber surface region, demonstrating that the precursor could diffuse and react to depths in excess of 100 nm into the surface of the polymer at 90 °C. Improved understanding of specific precursor/polymer reaction pathways can be important to optimize the performance of conformal inorganic thin film coatings on polymers.}, number={20}, journal={JOURNAL OF MATERIALS CHEMISTRY}, author={Spagnola, Joseph C. and Gong, Bo and Arvidson, Sara A. and Jur, Jesse S. and Khan, Saad A. and Parsons, Gregory N.}, year={2010}, pages={4213–4222} } @article{peng_sun_spagnola_saquing_khan_spontak_parsons_2009, title={Bi-directional Kirkendall Effect in Coaxial Microtuble Nanolaminate Assemblies Fabricated by Atomic Layer Deposition}, volume={3}, ISSN={["1936-086X"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000264535200010&KeyUID=WOS:000264535200010}, DOI={10.1021/nn8006543}, abstractNote={The solid-state reaction within a coaxial Al2O3/ZnO/Al2O3 multilayered microtubular structure can be used to prepare discrete microtube-in-microtube ZnAl2O4 spinel assemblies through a Kirkendall void production mechanism at 700 degrees C. In contrast with previous studies of the nanoscale Kirkendall effect, the reaction observed here proceeds through a bi-directional vacancy diffusion mechanism wherein ZnO species diffuse into inner- and outer-Al2O3 concentric layers, thereby resulting in vacancy supersaturation and void production between two isolated spinel microtubes. Low-temperature atomic layer deposition (ALD) of Al2O3 and ZnO enables the fabrication of complex coaxial multilayered microtubes with precise control of the starting film thicknesses and relative composition. When a molar excess of ZnO is present between two Al2O3 layers, electron microscopy images reveal incomplete ZnO consumption after annealing at 700 degrees C. At higher initial Al2O3 concentrations, however, complete reaction with ZnO is observed, and the size of the Kirkendall gap between isolated spinel microtubes appears to be directly influenced by the thickness of the intermediate ZnO layer.}, number={3}, journal={ACS NANO}, author={Peng, Qing and Sun, Xiao-Yu and Spagnola, Joseph C. and Saquing, Carl and Khan, Saad A. and Spontak, Richard J. and Parsons, Gregory N.}, year={2009}, month={Mar}, pages={546–554} } @article{saquing_manasco_khan_2009, title={Electrospun Nanoparticle-Nanofiber Composites via a One-Step Synthesis}, volume={5}, ISSN={1613-6810 1613-6829}, url={http://dx.doi.org/10.1002/smll.200801273}, DOI={10.1002/smll.200801273}, abstractNote={Abstract}, number={8}, journal={Small}, publisher={Wiley}, author={Saquing, Carl D. and Manasco, Joshua L. and Khan, Saad A.}, year={2009}, month={Apr}, pages={944–951} } @article{gupta_saquing_afshari_tonelli_khan_kotek_2009, title={Porous Nylon-6 Fibers via a Novel Salt-Induced Electrospinning Method}, volume={42}, ISSN={["1520-5835"]}, DOI={10.1021/ma801918c}, abstractNote={Porous nylon-6 fibers are obtained from Lewis acid-base complexation of gallium trichloride (GaCl3) and nylon-6 using electrospinning followed by GaCl3 removal. DSC and FTIR results reveal that the electrospun fibers, prior to GaCl3 removal, are amorphous with no hydrogen bonds present between nylon-6 chains. GaCl3 being a Lewis acid interacts with the Lewis base sites (CdO groups) on the nylon-6 chains, thereby preventing the chains to crystallize via intermolecular hydrogen bonding. Subsequent removal of GaCl3 from the as-spun fibers by soaking the electrospun web in water for 24 h leads to the formation of pores throughout the fibers. While the average fiber diameter remains effectively the same after salt removal, the average surface area increases by more than a factor of 6 for the regenerated fibers. The dual use of a metal salt (Lewis acid) to (a) facilitate fiber formation by temporary removal of polymer interchain interactions and (b) act as a porogen provides a facile approach to obtain porous fibers via electrospinning.}, number={3}, journal={MACROMOLECULES}, author={Gupta, Amit and Saquing, Carl D. and Afshari, Mehdi and Tonelli, Alan E. and Khan, Saad A. and Kotek, Richard}, year={2009}, month={Feb}, pages={709–715} } @article{talwar_harding_oleson_khan_2009, title={Surfactant-Mediated Modulation of Hydrophobic Interactions in Associative Polymer Solutions Containing Cyclodextrin}, volume={25}, ISSN={["0743-7463"]}, DOI={10.1021/la803056e}, abstractNote={The ability of nonionic surfactants to modulate the rheological characteristics of comblike hydrophobically modified associative polymer solutions containing cyclodextrin (CD) is examined. Addition of either alpha- or beta-CD to these polymers results in a marked decrease in solution viscosity and viscoelastic properties because of the encapsulation of the polymer hydrophobes by CD. Nonionic surfactants, introduced to such a system, alter the hydrophobic interactions by competing with the polymer hydrophobes for complexation with the CDs. In this regard, nonylphenol ethoxylates (NPe) with different ethylene oxide chain lengths, which determine the hydrophilic-lipophilic balance (HLB) of the surfactant, are used. Our results reveal that the extent and rate of recovery of zero shear viscosity as well as dynamic moduli are strongly influenced by the type of CD (alpha versus beta) as well as the HLB of the surfactant. For polymer solutions containing alpha-CD, recovery is observed solely in the presence of a low-HLB surfactant (NP6 and NP8). Additionally, in the case of NP6, the viscosity increases monotonically above the original hydrophobically modified alkali-soluble emulsion viscosity with surfactant addition, whereas for that of a higher HLB surfactant (NP15), the viscosity shows no appreciable change. In the case of beta-CD, on the other hand, a complete recovery as well as further enhancement of rheological properties is achieved using the above surfactants. However, the trends of viscosity modulation are dissimilar for different surfactants as we witness a monotonous increase in the case of NP6 while a maximum in viscosity is observed in the presence of NP8 and NP15. The contrasting observations can be explained in terms of varying affinities of alpha- and beta-CDs to bind with NP surfactants and the existence of different micellar structures in solution as governed by surfactant HLB. These results are further confirmed by UV/vis spectroscopy and cloud point measurements.}, number={2}, journal={LANGMUIR}, author={Talwar, Sachin and Harding, Jonathon and Oleson, Keith R. and Khan, Saad A.}, year={2009}, month={Jan}, pages={794–802} } @article{talwar_hinestroza_pourdeyhimi_khan_2008, title={Associative polymer facilitated electrospinning of nanofibers}, volume={41}, ISSN={["1520-5835"]}, DOI={10.1021/ma8004795}, abstractNote={Electrospun nanofibers present an exciting avenue for development of novel materials with well-defined functionalities; however, broadening the scope of electrospinning to a diverse range of polymers remains a major challenge. In particular, a recurring issue in this field is the inability to spin polymers at lower concentrations in order to achieve smaller fiber diameters. This work explores the use of associative polymers as a means to overcome this limiting factor that prevents the electrospinnning of nanofibers from low-concentration polymer solutions. Hydrophobically modified alkali-soluble emulsion (HASE) polymers are comblike associative polymers with pendant hydrophobes that form a network in aqueous media consisting of both intra- and intermolecular hydrophobic junctions. Rheological measurements reveal that addition of HASE polymers in small amounts to poly(ethylene oxide) solutions leads to considerable increase in viscosity as well as dynamic moduli of the system. More importantly, these rheol...}, number={12}, journal={MACROMOLECULES}, author={Talwar, Sachin and Hinestroza, Juan and Pourdeyhimi, Benham and Khan, Saad A.}, year={2008}, month={Jun}, pages={4275–4283} } @article{talwar_scanu_raghavan_khan_2008, title={Influence of binary surfactant mixtures on the rheology of associative polymer solutions}, volume={24}, ISSN={["0743-7463"]}, DOI={10.1021/la801030n}, abstractNote={Hydrophobically modified alkali-soluble emulsion polymers (HASE) are a class of comblike associative polymers that can impart high viscosities to aqueous solutions. The rheology of HASE solutions can be tuned by the addition of surfactants, such as nonylphenol ethoxylates (NP e), where e is the length of the hydrophilic (ethoxylate) chain. While previous studies have considered individual surfactants, our focus here is on binary surfactant mixtures. We find that equimolar NP4-NP12 mixtures significantly enhance the zero-shear viscosities of HASE solutions as compared to equivalent amounts of NP8, especially at high overall surfactant concentrations. Dynamic rheological measurements suggest that the higher viscosities are due to increases in the lifetime of hydrophobic junctions in the polymer-surfactant network. In contrast to the above results, equimolar NP4-NP8 mixtures are rheologically identical to equivalent solutions of NP6. The differences between the two sets of mixtures are further correlated with cloud point measurements and thereby with the overall hydrophilic-lipophilic balance (HLB) of the surfactant system.}, number={15}, journal={LANGMUIR}, author={Talwar, Sachin and Scanu, Lauriane and Raghavan, Srinivasa R. and Khan, Saad A.}, year={2008}, month={Aug}, pages={7797–7802} } @article{ji_saquing_khan_zhang_2008, title={Preparation and characterization of silica nanoparticulate-polyacrylonitrile composite and porous nanofibers}, volume={19}, ISSN={["1361-6528"]}, url={https://publons.com/publon/7178323/}, DOI={10.1088/0957-4484/19/8/085605}, abstractNote={In this study, polyacrylonitrile (PAN) composite nanofibers containing different amounts of silica nanoparticulates have been obtained via electrospinning. The surface morphology, thermal properties and crystal structure of PAN/silica nanofibers are characterized using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, wide-angle x-ray diffraction (WAXD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The results indicate that the addition of silica nanoparticulates affects the structure and properties of the nanofibers. In addition to PAN/silica composite nanofibers, porous PAN nanofibers have been prepared by selective removal of the silica component from PAN/silica composite nanofibers using hydrofluoric (HF) acid. ATR-FTIR and thermal gravimetric analysis (TGA) experiments validate the removal of silica nanoparticulates by HF acid, whereas SEM and TEM results reveal that the porous nanofibers obtained from composite fibers with higher silica contents exhibited more nonuniform surface morphology. The Brunauer–Emmett–Teller (BET) surface area of porous PAN nanofibers made from PAN/silica (5 wt%) composite precursors is higher than that of pure nonporous PAN nanofibers.}, number={8}, journal={NANOTECHNOLOGY}, publisher={IOP Publishing}, author={Ji, Liwen and Saquing, Carl and Khan, Saad A. and Zhang, Xiangwu}, year={2008}, month={Feb} } @article{frankowski_khan_spontak_2007, title={Chain-scission-induced intercalation as a facile route to polymer nanocomposites}, volume={19}, ISSN={["1521-4095"]}, DOI={10.1002/adma.200600793}, abstractNote={Polymer/clay nanocomposites (NCs) prepared using melt intercalation must be properly formulated and processed to achieve intercalation or exfoliation. Organically modified layered silicates (OMLSs) are often used to permit polymer intercalation and thereby separate the silicate platelets. Prior modeling efforts suggest that high-molecular-weight (HMW) polymers tend to yield immiscible NCs unlike their low-molecular-weight (LMW) analogs, which commonly result in exfoliated or intercalated NCs. Although formulations containing LMW polar additives (e.g., maleic anhydride copolymers) have succeeded in producing at least partially exfoliated rather than immiscible NCs, a need persists for simpler HMW formulations in order to expedite industrial scale-up. The present study examines blends composed of HMW polystyrene (PS) and an OMLS that remains largely immiscible when annealed under an inert N2 atmosphere with little or no shear. Controlled thermal-oxidative chain scission of the HMW PS in an O2-rich environment promotes intercalation of short PS chains within the OMLS, thereby expanding and disordering the platelets as an intercalated NC develops. This scission-induced intercalation mechanism ensures that the resultant NC is in a thermodynamically stable state unlike NCs prepared using in situ polymerization, which may deintercalate during further processing. Moreover, scission intercalation may be used as a general means by which to promote intercalation or possibly exfoliation in previously reported immiscible NCs. Polymeric NCs containing clay have become an increasingly important topic in the development of lightweight, tough, and impermeable materials since the Toyota research laboratories polymerized nylon-6 in the presence of sodium montmorillonite (Na-MMT) for automotive applications in the late 1980s. In situ polymerization has enjoyed the most success in producing exfoliated NCs wherein individual clay platelets are uniformly dispersed in a polymeric matrix, because the polymer chains can grow within the silicate galleries. Another NC-fabrication strategy is solution intercalation, in which polymer, solvent, and clay are mixed together. In this case, confinement of polymer chains upon diffusion into the silicate galleries is compensated for by the entropic gain caused by desorbed solvent molecules. Both in situ polymerization and solution intercalation typically require relatively large quantities of organic solvent, whereas melt intercalation relies on annealing above the glass-transition (Tg) or melting (Tm) temperature of the polymer matrix under static or shear conditions. Melt intercalation constitutes an environmentally benign and commercially feasible process that successfully yields intercalated or exfoliated NCs from more polymer–clay pairs than either in situ polymerization or solution intercalation. Giannelis and co-workers have previously demonstrated that sieved PS powder can intercalate into fluorohectorite under static annealing in an inert N2 atmosphere at 180 °C and below. At molecular weights comparable to that of the PS used in the present study (weight-average molecular weight, Mw, 330 kg mol ), noticeable intercalation requires approximately six hours. This result reflects their observation that the diffusion of PS into the silicate galleries under quiescent conditions becomes increasingly difficult with increasing chain length. Complementary studies have shown that twin-screw extrusion of HMW PS and OMLS with optimized screw profiles can overcome diffusion limits associated with static annealing at high temperatures, as well as circumvent undesirable dispersion issues. Under routine operating conditions, however, we expect sufficient concentrations of O2 to be present [31] for thermal-oxidative chain scission to occur. Indeed, an increase in temperature or addition of clay have been independently found to increase the rate of PS chain scission in the melt. Although most studies do not report Mw for the polymer after extrusion, we propose that the sequential chain-scission–intercalation mechanism described below may be at least partially responsible for the intercalation of polymer into OMLSs and the corresponding formation of NCs from HMW PS. Our system was designed to be commercially relevant as resins are usually obtained in pellet form and the screw of an extruder may not always be optimized for clay intercalation because of multiple products being run on a common manufacturing line. Single-screw extrusion of HMW PS and Cloisite 15A OMLS at a melt temperature of 185 °C yielded an immiscible NC according to X-ray diffractometry (XRD). As discussed later, extruded PS/OMLS exhibited a principal peak C O M M U N IC A TI O N}, number={9}, journal={ADVANCED MATERIALS}, author={Frankowski, David J. and Khan, Saad A. and Spontak, Richard J.}, year={2007}, month={May}, pages={1286-+} } @article{bronstein_karlinsey_yi_carini_werner-zwanziger_konarev_svergun_sanchez_khan_2007, title={Composite solid polymer electrolytes based on pluronics: Does ordering matter?}, volume={19}, ISSN={["1520-5002"]}, DOI={10.1021/cm7022218}, abstractNote={Composite solids polymer electrolytes (SPEs) based on Pluronic block copolymers, PEOx-b-PPOy-b-PEOx, and silicate organic–inorganic component (OIC) formed in situ have been synthesized and characte...}, number={25}, journal={CHEMISTRY OF MATERIALS}, author={Bronstein, Lyudmila M. and Karlinsey, Robert L. and Yi, Zheng and Carini, John and Werner-Zwanziger, Ulli and Konarev, Peter V. and Svergun, Dmitri I. and Sanchez, Angelica and Khan, Saad}, year={2007}, month={Dec}, pages={6258–6265} } @article{mahammad_roberts_khan_2007, title={Cyclodextrin - hydrophobe complexation in associative polymers}, volume={3}, ISSN={["1744-683X"]}, DOI={10.1039/b700167c}, abstractNote={We develop a new rheology-based method to study the complexation of cyclodextrins with hydrophobes in hydrophobically modified associative polymer solutions. The associative polymers have comb-like structure with hydrophobic groups randomly attached to the polymer backbone. Intermolecular interactions between the hydrophobic groups form a transient network resulting in thickening of the polymer solutions. On addition of cyclodextrins (CD) to the solution, the hydrophobes are encapsulated within the hydrophobic cavity of the cyclodextrins. This reduces viscoelastic properties of the polymer solution by several orders of magnitude. We exploit the existence of a dynamic equilibrium between CD adsorbed to the hydrophobes and free CD in the solution, to develop a rheology-based Langmuir-type adsorption isotherm for estimating the binding constant for molecular complexation. The model is based on the assumption that the amount of CD adsorbed is proportional to the reduction in elastic modulus of the polymer solution due to the encapsulation of the network junctions by CD. The effects of temperature on binding constant are studied to estimate the enthalpy and entropy of complexation. Experiments are conducted with both α-and β-CD at different polymer concentrations and temperatures to estimate the relative strength of binding of the CDs. At a given temperature and a polymer concentration, α-CD has a lower binding constant compared to that of β-CD, indicating higher affinity of α-CD to adsorb onto the hydrophobes. Since α-CDs have a smaller ring size, they can snugly fit to the hydrophobes and the association leads to higher enthalpy and entropy change.}, number={9}, journal={SOFT MATTER}, author={Mahammad, Shamsheer and Roberts, George W. and Khan, Saad A.}, year={2007}, pages={1185–1193} } @article{mahammad_comfort_kelly_khan_2007, title={Rheological properties of guar galactomannan solutions during hydrolysis with galactomannanase and alpha-galactosidase enzyme mixtures}, volume={8}, ISSN={["1526-4602"]}, DOI={10.1021/bm0608232}, abstractNote={Guar galactomannan, a naturally occurring polysaccharide, is susceptible to hydrolysis by three enzymes: beta-mannosidase, beta-mannanase, and alpha-galactosidase. The beta-mannosidase cleaves a single mannose unit from the nonreducing end of the guar molecule, the beta-mannanase cleaves interior glycosidic bonds between adjacent mannose units, and the alpha-galactosidase cleaves the galactose side branches off the guar. In this study, hydrolysis of guar solutions using hyperthermopilic versions of these enzymes together in different proportions and combinations are examined. The enzymatic reactions are carried out in situ in a rheometer, and the progress of the reaction is monitored through measuring the variation in zero shear viscosity. We find the presence of alpha-galactosidase to affect the action of both beta-mannanase and beta-mannosidase with respect to solution rheology. However, this effect is more pronounced when the alpha-galactosidase and beta-mannanase or beta-mannosidase enzymes were added sequentially rather than simultaneously. This likely is the result of debranching of the guar, which facilitates attack on beta-1,4-linkages by both the beta-mannanase and the beta-mannosidase enzymes and increases hydrolytic rates by the individual enzymes. A rheology-based kinetic model is developed to estimate the reaction rate constants and interpret synergistic effects of multiple enzyme contributions. The model fits the experimental data well and reveals that both the native and the debranched guar have the same activation energy for beta-mannanase action, although debranching considerably increases the frequency of enzyme-guar interactions.}, number={3}, journal={BIOMACROMOLECULES}, author={Mahammad, Shamsheer and Comfort, Donald A. and Kelly, Robert M. and Khan, Saad A.}, year={2007}, month={Mar}, pages={949–956} } @article{frankowski_capracotta_martin_khan_spontak_2007, title={Stability of organically modified montmorillonites and their polystyrene nanocomposites after prolonged thermal treatment}, volume={19}, ISSN={["0897-4756"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34250177310&partnerID=MN8TOARS}, DOI={10.1021/cm061953k}, abstractNote={Melt intercalation of montmorillonite (MMT) into polymeric matrices to improve the mechanical properties of polymers has evolved into a subject of tremendous fundamental and technological interest....}, number={11}, journal={CHEMISTRY OF MATERIALS}, author={Frankowski, David J. and Capracotta, Michael D. and Martin, James D. and Khan, Saad A. and Spontak, Richard J.}, year={2007}, month={May}, pages={2757–2767} } @article{appaw_gilbert_khan_2007, title={Viscoelastic behavior of cellulose acetate in a mixed solvent system}, volume={8}, ISSN={["1526-4602"]}, DOI={10.1021/bm0611681}, abstractNote={The effect of increasing water composition on the rheological and microstructural behavior of a ternary cellulose acetate (CA)/N,N-dimethylacetamide (DMA)/water system is examined. Addition of water to the CA/DMA system results in enhanced steady shear viscosity and dynamic viscoelastic properties and ultimately to phase-separated gel formation. The changes in dynamic rheological behavior of the system during gelation correlate well with the combined solubility parameter (delta) and, in particular, the Hansen hydrogen-bonding solubility parameter index (delta(h)) of the solvent system, suggesting hydrogen-bonding interactions may be the major route initiating the sol-gel process. For all gels studied, the elastic modulus and the critical stress to yield shifts to higher values with increasing CA concentration and/or water content. In addition, the elastic modulus exhibits a power-law behavior with water content, with the same power-law exponent observed for gels containing different CA concentrations. Addition of water leads to formation of a denser gel network, as evidenced from direct visualization of the gel microstructure through confocal microscopy.}, number={5}, journal={BIOMACROMOLECULES}, author={Appaw, Collins and Gilbert, Richard D. and Khan, Saad A.}, year={2007}, month={May}, pages={1541–1547} } @article{li_yerian_khan_fedkiw_2006, title={Crosslinkable fumed silica-based nanocomposite electrolytes for rechargeable lithium batteries}, volume={161}, ISSN={["1873-2755"]}, DOI={10.1016/j.jpowsour.2006.06.015}, abstractNote={Electrochemical and rheological properties are reported of composite polymer electrolytes (CPEs) consisting of dual-functionalized fumed silica with methacrylate and octyl groups + low-molecular weight poly(ethylene glycol) dimethyl ether (PEGdm) + lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, lithium imide) + butyl methacrylate (BMA). The role of butyl methacrylate, which aids in formation of a crosslinked network by tethering adjacent fumed silica particles, on rheology and electrochemistry is examined together with the effects of fumed silica surface group, fumed silica weight percent, salt concentration, and solvent molecular weight. Chemical crosslinking of the fumed silica with 20% BMA shows a substantial increase in the elastic modulus of the system and a transition from a liquid-like/flocculated state to an elastic network. In contrast, no change in lithium transference number and only a modest decrease (factor of 2) on conductivity of the CPE are observed, indicating that a crosslinked silica network has minimal effect on the mechanism of ionic transport. These trends suggest that the chemical crosslinks occur on a microscopic scale, as opposed to a molecular scale, between adjacent silica particles and therefore do not impede the segmental mobility of the PEGdm. The relative proportion of the methacrylate and octyl groups on the silica surface displays a nominal effect on both rheology and conductivity following crosslinking although the pre-cure rheology is a function of the surface groups. Chemical crosslinked nanocomposite polymer electrolytes offer significant higher elastic modulus and yield stress than the physical nanocomposite counterpart with a small/negligible penalty of transport properties. The crosslinked CPEs exhibit good interfacial stability with lithium metal at open circuit, however, they perform poorly in cycling of lithium–lithium cells.}, number={2}, journal={JOURNAL OF POWER SOURCES}, author={Li, Yangxing and Yerian, Jeffrey A. and Khan, Saad A. and Fedkiw, Peter S.}, year={2006}, month={Oct}, pages={1288–1296} } @article{eissa_puhl_kadla_khan_2006, title={Enzymatic cross-linking of beta-lactoglobulin: Conformational properties using FTIR spectroscopy}, volume={7}, ISSN={["1526-4602"]}, DOI={10.1021/bm050928p}, abstractNote={In this study, we use FTIR spectroscopy to probe the conformational changes of beta-lactoglobulin (beta-LG)-the main constituent of whey proteins-as subjected to enzymatic cross-linking by transglutaminase. We investigate both the amide I region (1600-1700 cm(-1)) and the C-H stretching region (2800-3100 cm(-1)). In the amide I region, spectra of denatured conformations of beta-LG, known to be necessary for cross-linking, differ according to the denaturation procedure, i.e., chemical or thermal treatment. Denaturation by chemical denaturants, dithiothreitol (DTT) or beta-mercaptoethanol, show no effect on the alpha-helix, while shifting the monomer dimer equilibrium toward higher monomer concentration. On the other hand, denaturing by thermal treatment dissociates the beta-sheets in the native structure, leading to new intermolecular beta-sheets being formed. Preheated then enzyme cross-linked beta-LG molecules show very similar spectra in the amide I region to the molecules with no cross-linking, indicating minimal effects of the cross-links on the carbonyl stretching mode. However, chemically denatured (using beta-mercaptoethanol) then enzyme cross-linked beta-LG molecules show noticeable diminution in the alpha-helix band and formation of strong hydrogen-bonded intermolecular beta-sheets. In the C-H stretching region, preheated then enzyme cross-linked beta-LG molecules exhibit a different degree of exposure of aliphatic amino acids due to the enzyme action. The same behavior is observed for DTT-treated then enzyme cross-linked beta-LG molecules. Generally, the changes in the C-H stretching region clearly indicate that hydrophobic interactions are altered upon enzymatic cross-linking.}, number={6}, journal={BIOMACROMOLECULES}, author={Eissa, Ahmed S. and Puhl, Christa and Kadla, John F. and Khan, Saad A.}, year={2006}, month={Jun}, pages={1707–1713} } @article{mahammad_prud'homme_roberts_khan_2006, title={Kinetics of enzymatic depolymerization of guar galactomannan}, volume={7}, ISSN={["1525-7797"]}, DOI={10.1021/bm060333+}, abstractNote={A new mathematical model based on Michaelis Menten (MM) kinetics is developed to predict the changes in molecular weight distribution (MWD) during the enzymatic depolymerization of guar galactomannan. The model accounts for the effect of branching by considering the guar molecule as a substrate having three types of bonds with different MM kinetic parameters. The overall kinetics of the enzymatic reactions then can be represented in terms of composite kinetic parameters that are functions of the MM parameters for the individual bonds. The depolymerization is assumed to follow a random scission mechanism, in which an enzyme randomly attacks the substrate molecule at any one of the three types of bonds, and leaves the substrate on cleavage of the bond. Expressions for the variation in molecular weights during depolymerization are developed by applying moment generating techniques to the kinetic model. The model is evaluated against the complete MWD obtained using gel permeation chromatography. During the initial stages of depolymerization, the enzymatic reaction is in the zero-order regime of MM kinetics and the polydispersity index (PDI) increases with time. Subsequently, the PDI decreases as the depolymerization tends to follow first order kinetics. We also show that for a zero-order, random or nonrandom scission, the variation of PDI with time can exhibit a maximum. These analyses confirm that an increase in PDI during the depolymerization is not necessarily due to nonrandom scission, as previously concluded.}, number={9}, journal={BIOMACROMOLECULES}, author={Mahammad, Shamsheer and Prud'homme, Robert K. and Roberts, George W. and Khan, Saad A.}, year={2006}, month={Sep}, pages={2583–2590} } @article{eissa_khan_2006, title={Modulation of hydrophobic interactions in denatured whey proteins by transglutaminase enzyme}, volume={20}, ISSN={["1873-7137"]}, DOI={10.1016/j.foodhyd.2005.07.005}, abstractNote={The role of enzyme crosslinking in mediating formation of hydrophobic association in chemically denatured whey protein isolates (WPI) is examined. WPI samples denatured with dithiothreitol (DTT) and incubated at 50 °C with and without transglutaminase enzyme show dramatic differences in viscosity, with the viscosity of the sample exposed to enzyme being lower by several orders of magnitude than the sample without enzyme. Upon further exposure of both samples to sodium dodecyl sulfate (SDS) to eliminate hydrophobic interactions, we observe no change in the viscosity of the sample previously treated with enzyme, suggesting this sample to have minimal hydrophobic associations. In contrast, the sample without enzyme shows a dramatic drop in viscosity indicating it to have had substantial hydrophobic associations. A similar trend but to a lesser extent is observed at a higher WPI concentration. These results taken together suggest that the formation of enzyme catalyzed ε-(γ-glutamyl)lysine bonds attenuates hydrophobic interactions through steric hindrance and formation of compact molecules that limits exposure of the hydrophobic moieties.}, number={4}, journal={FOOD HYDROCOLLOIDS}, author={Eissa, AS and Khan, SA}, year={2006}, month={Jun}, pages={543–547} } @article{guo_abdala_may_lincoln_khan_prud'homme_2006, title={Rheology control by modulating hydrophobic and inclusion associations in modified poly(acrylic acid) solutions}, volume={47}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2006.03.006}, abstractNote={The rheology of modified poly(acrylic acid) (PAA) solutions can be tuned by controlling the inclusion interactions between α-cyclodextrins and alkyl hydrophobes. We demonstrate three modes of control: (1) using free cyclodextrins (CD) to displace hydrophobe–hydrophobe association in hydrophobically modified poly(acrylic acid) (HMPAA) polymers—which reduces fluid viscosity, (2) using competitive inclusion interactions where stronger SDS:CD binding can be used to ‘unmask’ CD:hydropobe inclusion interactions—which increases viscosity, and (3) employing HMPAA inclusion interactions with CD groups grafted to PAA chains (CDPAA)—which produces higher viscosities than purely hydrophobic association systems at the same concentration. The inclusion association between alkyl side-group in HMPAA and CD, either free or grafted onto PAA, obeys a 1-to-1 stoichiometry at low polymer concentrations (<1 wt%). In contrast to purely hydrophobically associating polymers, the CD:hydrophobe interaction is only binary, and, therefore, these associated networks should be ideal model systems to test theoretical predictions for associative fluids.}, number={9}, journal={POLYMER}, author={Guo, Xuhong and Abdala, Ahmed A. and May, Bruce L. and Lincoln, Stephen F. and Khan, Saad A. and Prud'homme, Robert K.}, year={2006}, month={Apr}, pages={2976–2983} } @article{dai_khan_kadla_2006, title={Transient rheological behavior of lyotropic (acetyl)(ethyl)cellulose/m-cresol solutions}, volume={13}, ISSN={["1572-882X"]}, DOI={10.1007/s10570-005-9027-y}, number={3}, journal={CELLULOSE}, author={Dai, Qizhou and Khan, Saad A. and Kadla, John F.}, year={2006}, month={Jun}, pages={213–223} } @article{burke_park_srinivasarao_khan_2005, title={A novel enzymatic technique for limiting drug mobility in a hydrogel matrix}, volume={104}, ISSN={["1873-4995"]}, DOI={10.1016/j.jconrel.2005.01.017}, abstractNote={An oral colon specific drug delivery platform has been developed to facilitate targetted release of therapeutic proteins as well as small molecule drugs. A simple enzymatic procedure is used to modify the molecular architecture of a lightly chemically crosslinked galactomannan hydrogel as well as a model drug-galactomannan oligomer conjugate, fluoroisocynate (FITC) tagged guar oligomer, to entrap the model drug. The enzyme-modified hydrogel retains the drug until it reaches the colonic environment where bacteria secrete enzymes (namely beta-mannanase) to degrade the gel and release the drug molecule. Laser scanning confocal microscopy combined with fluorescence recovery after photobleaching is used to quantify the diffusion of the drug conjugate. The diffusion coefficient of solutes in the lightly crosslinked galactomannan hydrogel is approximately equal to the diffusion coefficient in the guar solution for simple diffusional drug loading. After drug loading, alpha-galactosidase treatment generates additional physical crosslinks in the hydrogel matrix as well as between the drug-oligomer conjugate and the hydrogel, which reduces diffusion of the drug-oligomer conjugate significantly. Degradation of the hydrogel by beta-mannanase results in a slow and controlled rate of FITC-guar oligomer diffusion, which generates an extended release profile for the model drug.}, number={1}, journal={JOURNAL OF CONTROLLED RELEASE}, author={Burke, MD and Park, JO and Srinivasarao, M and Khan, SA}, year={2005}, month={May}, pages={141–153} } @article{eissa_khan_2005, title={Acid-induced gelation of enzymatically modified, preheated whey proteins}, volume={53}, ISSN={["1520-5118"]}, DOI={10.1021/jf047957w}, abstractNote={Low-pH whey protein gels are formulated using a sequential protocol of heat treatment, enzyme incubation, and cold-set acidification. The heat-induced disulfide and enzyme-catalyzed epsilon-(gamma-glutamyl)lysine linkages, both at neutral pH, produce a polymerized protein solution. The molecular weights of these samples show an exponential increase with protein concentration. The additional enzyme-catalyzed cross-links cause little change in molecular weight from that of heat-treated samples at low protein concentrations, indicating predominant intramolecular cross-linking. Enzyme treatment at higher protein concentration however causes increase in molecular weight, possibly due to formation of intermolecular cross-links. Acidification of the polymerized protein solutions through glucono-delta-lactone acid leads to gel formation at pH 4. The elastic (G') and viscous (G' ') moduli of gels with and without enzyme treatment show similar frequency dependence, indicating comparable microstructures, consistent with all samples exhibiting similar fractal dimensions of approximately 2 obtained independently using rheology and confocal microscopy. A substantial increase in fracture strain and stress of the gel is achieved by enzyme treatment. However, the elastic modulus (G') is only slightly larger after enzyme treatment compared with heat-treated samples. These results indicate that factors responsible for fracture properties may not be apparent in the gel microstructure and linear viscoelastic properties.}, number={12}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Eissa, AS and Khan, SA}, year={2005}, month={Jun}, pages={5010–5017} } @misc{kelly_khan_leduc_tayal_prud'homme_2005, title={Compositions for fracturing subterranean formations}, volume={6,936,454}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Kelly, R. M. and Khan, S. A. and Leduc, P. and Tayal, A. and Prud'homme, R. K.}, year={2005} } @article{siripurapu_desimone_khan_spontak_2005, title={Controlled foaming of polymer films through restricted surface diffusion and the addition of nanosilica particles or CO2-philic surfactants}, volume={38}, ISSN={["1520-5835"]}, DOI={10.1021/ma047991b}, abstractNote={Synergistic use of surface barriers and nanoscale additives is investigated as alternate means by which to promote bubble nucleation in, and thus improve the porosity of, poly(methyl methacrylate) (PMMA) thin films (i) constrained between impenetrable plates, (ii) modified with either nanosilica particles, commercial short-chain fluorosurfactants, or designer CO2-philic block/graft copolymers, and (iii) exposed to high-pressure CO2. Resultant foamed films exhibit a vast array of micro/mesocellular morphologies in the presence of supercritical, as well as liquid, CO2 and demonstrate that copolymer micelles afford better control over bubble nucleation (with pore cell densities, N, approaching 1012 cells/cm3) relative to hard nonporous nanoparticles, which alone increase N by more than 2 orders of magnitude at low CO2 pressures. Incorporation of these nanoscale additives in a surface-constrained polymer matrix serves to enhance foaming through concurrent restriction of CO2 diffusion, heterogeneous nucleation...}, number={6}, journal={MACROMOLECULES}, author={Siripurapu, S and DeSimone, JM and Khan, SA and Spontak, RJ}, year={2005}, month={Mar}, pages={2271–2280} } @article{guo_abdala_may_lincoln_khan_prud'homme_2005, title={Novel associative polymer networks based on cyclodextrin inclusion compounds}, volume={38}, ISSN={["1520-5835"]}, DOI={10.1021/ma050071o}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVNoteNovel Associative Polymer Networks Based on Cyclodextrin Inclusion CompoundsXuhong Guo, Ahmed A. Abdala, Bruce L. May, Stephen F. Lincoln, Saad A. Khan, and Robert K. Prud'hommeView Author Information Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544; Departmant of Chemistry, University of Adelaide, Adelaide, SA 5005, Australia; and Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905 Cite this: Macromolecules 2005, 38, 7, 3037–3040Publication Date (Web):March 8, 2005Publication History Received12 January 2005Published online8 March 2005Published inissue 1 April 2005https://doi.org/10.1021/ma050071oCopyright © 2005 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1678Altmetric-Citations81LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (154 KB) Get e-AlertsSUBJECTS:Hydrophobicity,Macrocyclic compounds,Oligosaccharides,Polymers,Viscosity Get e-Alerts}, number={7}, journal={MACROMOLECULES}, author={Guo, XH and Abdala, AA and May, BL and Lincoln, SF and Khan, SA and Prud'homme, RK}, year={2005}, month={Apr}, pages={3037–3040} } @article{veleva_khan_cooper_2005, title={Oxidative and hydrolytic stability of a novel acrylic terpolymer for biomedical applications}, volume={74A}, ISSN={1549-3296 1552-4965}, url={http://dx.doi.org/10.1002/jbm.a.30349}, DOI={10.1002/jbm.a.30349}, abstractNote={Abstract}, number={1}, journal={Journal of Biomedical Materials Research Part A}, publisher={Wiley}, author={Veleva, Anka N. and Khan, Saad A. and Cooper, Stuart L.}, year={2005}, pages={117–123} } @article{mccormick_carol_khan_2005, title={The dynamics of single chains within a model polymer melt}, volume={122}, number={11}, journal={Journal of Chemical Physics}, author={McCormick, J. A. and Carol, K. H. and Khan, S. A.}, year={2005}, month={Mar} } @article{mccormick_hall_khan_2005, title={The dynamics of single chains within a model polymer melt}, volume={122}, ISSN={0021-9606 1089-7690}, url={http://dx.doi.org/10.1063/1.1863852}, DOI={10.1063/1.1863852}, abstractNote={Discontinuous molecular dynamics simulations are performed on a system containing 32 hard chains of length 192 at a volume fraction of ϕ=0.45 to explore the idea that localized entanglements have a significant effect on the dynamics of the individual chains within an entangled polymer melt. Anomalous behavior can still be observed when studying the dynamics of the individual chains, although increased time averaging causes the anomalous relaxation-memory-release behavior that was observed previously in the system to smooth out. First, the individual chain mean squared displacements and apparent diffusion coefficients are calculated, and a wide distribution of diffusive behavior is found. Although the apparent diffusion coefficient curve averaged over all chains displays the predicted long-time diffusive behavior, the curves for the individual chains differ both qualitatively and quantitatively. They display superdiffusive, diffusive, and subdiffusive behavior, with the largest percentage of chains exhibiting superdiffusive behavior and the smallest percentage exhibiting the predicted diffusive behavior. Next, the individual chain end-to-end vector autocorrelation functions and relaxation times are determined, and a wide distribution of stress relaxation behavior is found. The times when the end-to-end vector autocorrelation functions relax completely span almost an order of magnitude in reduced time. For some chains, the end-to-end vector autocorrelation function relaxes smoothly toward zero similar to the system average; however, for other chains the relaxation is slowed greatly, indicating the presence of additional entanglements. Almost half of the chains exhibit the anomalous behavior in the end-to-end vector autocorrelation function. Finally, the dynamic properties are displayed for a single chain exhibiting anomalous relaxation-memory-release behavior, supporting the idea that the relaxation-memory-release behavior is a single-chain property.}, number={11}, journal={The Journal of Chemical Physics}, publisher={AIP Publishing}, author={McCormick, Julie A. and Hall, Carol K. and Khan, Saad A.}, year={2005}, month={Mar}, pages={114902} } @article{li_zhang_khan_fedkiw_2004, title={Attenuation of Aluminum Current Collector Corrosion in LiTFSI Electrolytes Using Fumed Silica Nanoparticles}, volume={7}, ISSN={1099-0062}, url={http://dx.doi.org/10.1149/1.1756857}, DOI={10.1149/1.1756857}, abstractNote={Linear sweep voltammetry and electrochemical impedance spectroscopy were used to investigate the corrosion behavior of an aluminum current collector in contact with polymer solvent containing lithium bis(trifluoromethanesulfonyl)imide [LiN(CF 3 SO 2 ) 2 , LiTFSI] at room temperature. The electrolytes were liquid poly(ethylene glycol) dimethyl ether (Mw 250) + LiTFSI (Li:O ratio of 1:20), and composite gel electrolytes consisting of the baseline liquid electrolyte + 10 wt% fumed silica nanoparticles. Such electrolytes have potential utility in lithium-based rechargeable cells, although LiTFSI is known to affect corrosion of the commonly employed aluminum current collector. The electrochemical data indicate that aluminum corrosion is attenuated in the Presence of fumed silica nanoparticles. Possible mechanisms are discussed.}, number={8}, journal={Electrochemical and Solid-State Letters}, publisher={The Electrochemical Society}, author={Li, Yangxing and Zhang, Xiang-Wu and Khan, Saad A. and Fedkiw, Peter S.}, year={2004}, pages={A228} } @article{frankowski_fournier-bidoz_manners_ozin_khan_spontak_2004, title={Cover Picture: Macromol. Chem. Phys. 18/2004}, volume={205}, ISSN={1022-1352 1521-3935}, url={http://dx.doi.org/10.1002/macp.200490043}, DOI={10.1002/macp.200490043}, abstractNote={Cover: Surface‐constrained foaming of poly(ferrocenylsilane) ceramic precursor films with supercritical CO2 yields tunable microcellular foams that exhibit conventional isotropic pore cells (inset), as well as anisotropic pore cells that elongate and orient along preferred diffusion pathways.}, number={18}, journal={Macromolecular Chemistry and Physics}, publisher={Wiley}, author={Frankowski, David J. and Fournier-Bidoz, S�bastien and Manners, Ian and Ozin, Geoffrey A. and Khan, Saad A. and Spontak, Richard J.}, year={2004}, month={Dec}, pages={2381–2381} } @article{yerian_khan_fedkiw_2004, title={Crosslinkable fumed silica-based nanocomposite electrolytes: role of methacrylate monomer in formation of crosslinked silica network}, volume={135}, ISSN={["0378-7753"]}, DOI={10.1016/j.jpowsour.2004.03.064}, abstractNote={The electrochemical and rheological properties of composite polymer electrolytes (CPEs) based on fumed silica with tethered crosslinkable groups are reported. These silica nanoparticles are dispersed in electrolytes consisting of poly(ethylene glycol) dimethyl ether (PEGdm)+lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to which various methacrylate monomers, such as methyl (MMA), ethyl (EMA), butyl (BMA), n-hexyl (HMA), and n-dodecyl (DMA) methacrylate, are added. The methacrylate monomer facilitates creation of chemical crosslinks between fumed silica particles and formation of a crosslinked network. In this study, the effects of concentration and alkyl chain length of the monomers on conductivity, dynamic rheology, open-circuit interfacial stability, and cell voltage in lithium–lithium cell cycling are examined. Increasing the length of the monomer alkyl chain enhances both conductivity and elastic modulus of the crosslinked CPE. In contrast, increasing monomer concentration results in higher elastic modulus, but reduced conductivity. Lithium–lithium cell cycling and open-circuit interfacial stability results did not correlate with alkyl chain length. That is, for the lithium–lithium cycling studies, all crosslinked samples exhibit higher half-cycle voltage compared to non-crosslinked samples; however, the open-circuit interfacial stability of CPEs containing BMA and HMA exhibit improved stability compared to the other monomers and the CPE without monomer.}, number={1-2}, journal={JOURNAL OF POWER SOURCES}, author={Yerian, JA and Khan, SA and Fedkiw, PS}, year={2004}, month={Sep}, pages={232–239} } @article{frankowski_raez_manners_winnik_khan_spontak_2004, title={Formation of dispersed nanostructures from poly(ferrocenyldimethylsilane-b-dimethylsiloxane) nanotubes upon exposure to supercritical carbon dioxide}, volume={20}, ISSN={["0743-7463"]}, DOI={10.1021/la049646l}, abstractNote={While incompatible block copolymers commonly assemble into several established classical or complex morphologies, highly asymmetric poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS-b-PDMS) diblock copolymers can also self-organize into high-aspect-ratio nanotubes with PDMS corona in the presence of PDMS-selective organic solvents. Exposure of these nanotubes on a carbon substrate to supercritical carbon dioxide (scCO2), also a PDMS-selective solvent, appears to promote partial dissolution of the copolymer molecules. At sufficiently high copolymer concentrations, the dissolved molecules subsequently re-organize within the scCO2 environment to form new copolymer nanostructures that redeposit on the substrate upon scCO2 depressurization. Transmission electron microscopy reveals that micelles form under all the conditions examined here, whereas nanotubes coalesce and vesicles develop only at relatively high temperatures. The extent to which the copolymer nanotubes dissolve and the size distribution of the replacement micelles are sensitive to exposure conditions. These results suggest that the phase behavior of PFS-b-PDMS diblock copolymers in scCO2 may be remarkably rich and easily tunable.}, number={21}, journal={LANGMUIR}, author={Frankowski, DJ and Raez, J and Manners, I and Winnik, MA and Khan, SA and Spontak, RJ}, year={2004}, month={Oct}, pages={9304–9314} } @article{zhang_li_khan_fedkiw_2004, title={Inhibition of lithium dendrites by fumed silica-based composite electrolytes}, volume={151}, ISSN={["1945-7111"]}, url={https://publons.com/publon/7178366/}, DOI={10.1149/1.1767158}, abstractNote={Lithium dendrite formation is investigated via in situ microscopy in a liquid electrolyte containing polyethylene glycol dimethyl ether 1 lithium bis~trifluoromethylsulfonyl !imide and composite gel-like electrolytes formed by dispersing nanometer-size fumed silica into the liquid. Fumed silicas with either hydrophilic silanol surface groups or hydrophobic octyl surface groups were employed. Dendrites with current density-dependent morphology are formed in liquid electrolyte but addition of fumed silica inhibits their formation, with hydrophilic fumed silica having a more pronounced effect than hydrophobic silica. The dendrite inhibition effect of fumed silica is attributed to its abilities to form a continuous network with elastic-like properties and scavenge impurities from the electrolyte.}, number={8}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, publisher={The Electrochemical Society}, author={Zhang, XW and Li, YX and Khan, SA and Fedkiw, PS}, year={2004}, pages={A1257–A1263} } @article{siripurapu_desimone_khan_spontak_2004, title={Low-temperature, surface-mediated foaming of polymer films}, volume={16}, ISSN={["1521-4095"]}, DOI={10.1002/adma.200306068}, abstractNote={Ultraporous thin polymer films (see Figure) are generated using physical constraints imposed by external surfaces (hard plates) and internal surfaces (hard nanoparticles and soft micelles) via foaming with supercritical CO2. The constraints serve as diffusion barriers and/or heterogeneous nucleation sites. Use of CO2‐philic copolymers further enables microcellular foaming at reduced pressures with liquid CO2.}, number={12}, journal={ADVANCED MATERIALS}, author={Siripurapu, S and DeSimone, JM and Khan, SA and Spontak, RJ}, year={2004}, month={Jun}, pages={989-+} } @misc{desimone_khan_royer_spontak_walker_gay_siripurapu_2004, title={Methods of making foamed materials of blended thermoplastic polymers using carbon dioxide}, volume={6,790,870}, number={2004 Sept. 14}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={DeSimone, J. M. and Khan, S. A. and Royer, J. R. and Spontak, R. J. and Walker, T. A. and Gay, Y. J. and Siripurapu, S.}, year={2004} } @article{zhang_khan_fedkiw_2004, title={Nanocomposite electrolytes using single-ion conducting fumed silica}, volume={7}, ISSN={["1944-8775"]}, url={https://publons.com/publon/7178367/}, DOI={10.1149/1.1792267}, abstractNote={Fumed silica surfaces were chemically modified to form single-ion conductors by attaching lithium-exchanged anionic groups (lithium 2-acrylamido-2-methyl-1-propanesulfonate, LiAMPS) to surface methacrylates on Degussa R711 fumed silica (abbreviated as R711-pLiAMPS). Surface lithium-ion contents varying from 0.7 to 9.1 nm - 2 were synthesized. Conductivity and transference number measurements were conducted on nanocomposite electrolytes containing polyethylene glycol dimethyl ether (PEGdm) + R711-pLiAMPS. A maximum room-temperature conductivity of 4.5 X 10 - 6 S cm - 1 was obtained at a surface Li + content of 4.2 nm - 2 and a Li:O mole ratio of 1:100 (15.8 wt % filler) with a Li + transference number of 0.59. A maximum Li + transference number of 0.78 was achieved at a surface Li + surface content of 4.2 nm - 2 and a Li:O mole ratio of 1:20 (48.5 wt % filler) with a conductivity of 2.2 X 10 - 6 S cm - 1 . Adding lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) to the samples enhances room-temperature conductivity by more than two orders of magnitude while still maintaining a relatively high Li + transference number.}, number={10}, journal={ELECTROCHEMICAL AND SOLID STATE LETTERS}, author={Zhang, XW and Khan, SA and Fedkiw, PS}, year={2004}, pages={A361–A364} } @article{eissa_bisram_khan_2004, title={Polymerization and gelation of whey protein isolates at low pH using transglutaminase enzyme}, volume={52}, ISSN={["1520-5118"]}, DOI={10.1021/jf0355304}, abstractNote={Dynamic and steady shear rheology is used to examine the synthesis of low-pH (approximately 4) whey protein gels obtained through a two-step process. The first step involves cross-linking of whey proteins at pH 8 and 50 degrees C using transglutaminase enzyme, while the second step entails cold-set acidification of the resulting solution using glucono-delta-lactone (GDL) acid. During the first step, the sample undergoes enzyme-catalyzed epsilon-(gamma-glutamyl)lysine bond formation with a substantial increase in viscosity. Acidification in the second step using GDL acid leads to a rapid decrease in pH with a concomitant increase in the elastic (G') and viscous (G' ') moduli and formation of a gelled network. We examine the large strain behavior of the gel samples using a relatively new approach that entails plotting the product of elastic modulus and strain (G'gamma) as a function of increasing dynamic strain and looking for a maximum, which corresponds to the yield or fracture point. We find the enzyme-catalyzed gels to have significantly higher yield/fracture stress and strain compared to cold-set gels prepared without enzyme or conventional heat-set gels. In addition, the elastic modulus of the enzyme-catalyzed gel is also higher than its non-enzyme-treated counterpart. These results are discussed in terms of the gel microstructure and the role played by the enzyme-induced cross-links.}, number={14}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, author={Eissa, AS and Bisram, S and Khan, SA}, year={2004}, month={Jul}, pages={4456–4464} } @article{quinones-hinojosa_chang_khan_lawton_mcdermott_2004, title={Renal Cell Carcinoma Metastatic to the Choroid Mimicking Intraventricular Meningioma}, volume={31}, ISSN={0317-1671 2057-0155}, url={http://dx.doi.org/10.1017/S0317167100002948}, DOI={10.1017/S0317167100002948}, abstractNote={Background:Metastatic renal cell carcinoma to the choroid plexus is a rare condition and can be easily confused with meningioma.}, number={1}, journal={Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques}, publisher={Cambridge University Press (CUP)}, author={Quinones-Hinojosa, Alfredo and Chang, Edward F. and Khan, Saad A. and Lawton, Michael T. and McDermott, Michael W.}, year={2004}, month={Feb}, pages={115–120} } @article{abdala_wu_olesen_jenkins_khan_tonelli_2004, title={Solution rheology of hydrophobically modified associative polymers: Effects of backbone composition and hydrophobe concentration}, volume={48}, ISSN={["1520-8516"]}, DOI={10.1122/1.1773781}, abstractNote={We investigate the effects of polymer molecular structure on the solution rheology of a hydrophobically modified associative polymer comprised of macromonomers with alkyl hydrophobes attached to a poly(ethyl acrylate-co-methacrylic acid) backbone. In particular, the effect of polymer backbone composition with variable proportions of methacrylic acid (MAA) and ethyl acrylate (EA) are examined. We find that the concentration of the MAA monomer has a large impact on polymer viscoelasticity. Polymers with low MAA content have smaller hydrodynamic size that result in lower viscosities and dynamic elastic moduli compared to polymers with high MAA content. Moreover, the balance between the polymer hydrodynamic size, the chain flexibility, and the aggregation of the EA blocks yield maxima in these material functions with respect to the MAA concentration. The scaling of shear viscosity, high frequency elastic modulus, and creep compliance with polymer concentration exhibits power-law behavior with different exponents. In all cases, three power-law regimes, regardless of the MAA content, are observed that can be attributed to the presence of different modes of hydrophobic interaction. However, the transitions shift to lower concentrations as the MAA content increases. With regards to the effects of the macromonomer side-chain concentration, we observe a substantial increase in viscosity at intermediate macromonomer content (1 mol %), possibly due to an increase in the number of intermolecular junctions as the number of hydrophobes per chain increases. This is in contrast to (i) low macromonomer concentration (0.3 mol %) behavior that reveals low viscosity due to weak hydrophobic associations, and (ii) high macromonomer concentration (1.9 mol %) behavior that favors more intramolecular association resulting in lower viscoelastic properties compared to intermediate macromonomer concentrations.We investigate the effects of polymer molecular structure on the solution rheology of a hydrophobically modified associative polymer comprised of macromonomers with alkyl hydrophobes attached to a poly(ethyl acrylate-co-methacrylic acid) backbone. In particular, the effect of polymer backbone composition with variable proportions of methacrylic acid (MAA) and ethyl acrylate (EA) are examined. We find that the concentration of the MAA monomer has a large impact on polymer viscoelasticity. Polymers with low MAA content have smaller hydrodynamic size that result in lower viscosities and dynamic elastic moduli compared to polymers with high MAA content. Moreover, the balance between the polymer hydrodynamic size, the chain flexibility, and the aggregation of the EA blocks yield maxima in these material functions with respect to the MAA concentration. The scaling of shear viscosity, high frequency elastic modulus, and creep compliance with polymer concentration exhibits power-law behavior with different expone...}, number={5}, journal={JOURNAL OF RHEOLOGY}, author={Abdala, A. A. and Wu, W. J. and Olesen, K. R. and Jenkins, R. D. and Khan, Saad and Tonelli, A. E.}, year={2004}, pages={979–994} } @article{siripurapu_coughlan_spontak_khan_2004, title={Surface-constrained foaming of polymer thin films with supercritical carbon dioxide}, volume={37}, ISSN={["1520-5835"]}, DOI={10.1021/ma0484983}, abstractNote={Microcellular polymer foams afford a wide variety of attributes relative to their dense analogues, and efforts remain underway to establish viable routes to generate foams with substantially reduced pore cell size and increased pore cell density. Barrier constraints are applied in the present work to achieve diffusion-controlled isothermal foaming of thin polymer films in the presence of supercritical carbon dioxide (scCO2). Poly(methyl methacrylate) (PMMA) films measuring ca. 95−100 μm in thickness are physically constrained between two impenetrable plates so that scCO2 exit diffusion is restricted to the film edges. Results obtained here demonstrate that the pore size can be systematically reduced to less than 100 nm in such systems by applying high saturation scCO2 pressures, relatively low foaming temperatures (near the glass transition temperature of the scCO2-plasticized polymer), and a rapid pressure quench. Classical nucleation theory (CNT) modified to account for the compressible nature of scCO2 ...}, number={26}, journal={MACROMOLECULES}, author={Siripurapu, S and Coughlan, JA and Spontak, RJ and Khan, SA}, year={2004}, month={Dec}, pages={9872–9879} } @article{singhal_capracotta_martin_khan_fedkiw_2004, title={Transport properties of hectorite based nanocomposite single ion conductors}, volume={128}, ISSN={["0378-7753"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-1542333424&partnerID=MN8TOARS}, DOI={10.1016/j.jpowsour.2003.09.064}, abstractNote={The ionic conductivity and rheological properties of clay filled nanocomposite electrolytes are reported. These electrolytes, which have potential use in lithium-ion batteries, consist of lithium-exchanged hectorite, a 2:1 layered smectite clay, dispersed in ethylene carbonate (EC) or a mixture of EC+polyethylene glycol di-methyl ether (PEG-dm, 250 MW). All samples exhibit elastic, gel-like characteristics and room temperature conductivities of order 0.1 mS/cm. A maximum in conductivity is observed at about 25 wt.% clay concentration. A maximum in hectorite basal layer spacing is also observed in the same concentration range, suggesting a direct correlation between conductivity and layer spacing. The elastic modulus and yield stress increase by two orders of magnitude and the conductivity increases by one order of magnitude with increase in hectorite concentration from 5 to 25%, which indicates the significant influence of hectorite content in determining the characteristics of these single-ion conductors. The solvent composition plays a secondary role in this regard, with addition of PEG-dm to the base EC+hectorite electrolyte producing moderate improvement in conductivity. Similarly, the addition of PEG-dm to EC+hectorite affects an increase by only a factor of three in the elastic modulus and yield stress of the electrolyte.}, number={2}, journal={JOURNAL OF POWER SOURCES}, author={Singhal, RG and Capracotta, MD and Martin, JD and Khan, SA and Fedkiw, PS}, year={2004}, month={Apr}, pages={247–255} } @article{frankowski_fournier-bidoz_manners_ozin_khan_spontak_2004, title={Tunable microcellular morphologies from poly (ferrocenylsilane) ceramic precursors foamed in supercritical CO(2)}, volume={205}, ISSN={["1022-1352"]}, DOI={10.1002/macp.200400333}, abstractNote={Abstract}, number={18}, journal={MACROMOLECULAR CHEMISTRY AND PHYSICS}, author={Frankowski, DJ and Fournier-Bidoz, SB and Manners, I and Ozin, GA and Khan, SA and Spontak, RJ}, year={2004}, month={Dec}, pages={2398–2408} } @misc{riley_fedkiw_khan_davies_2003, title={Composite electrolytes based on smectite clays and high dielectric organic liquids and electrodes}, volume={6,544,689}, number={2003 Apr. 8}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Riley, M. W. and Fedkiw, P. S. and Khan, S. A. and Davies, B.}, year={2003}, month={Apr} } @article{walls_riley_fedkiw_spontak_baker_khan_2003, title={Composite electrolytes from self-assembled colloidal networks}, volume={48}, ISSN={["0013-4686"]}, DOI={10.1016/S0013-4686(03)00187-7}, abstractNote={In this study, we present two approaches to developing composite electrolytes exploiting the self-assembling nature of colloidal fillers. The first system comprises of oligomers of poly(ethylene glycol) dimethyl ether, branched fumed silica particulates and lithium salt. The fumed silica forms a three-dimensional, self-supporting network that provides mechanical stability. The large pores of the network has little effect on diffusivity of ions and oligomers, lithium transference number and ionic conductivity, with the latter showing values >10−3 S/cm at ambient conditions. The second system consists of Li exchanged hectorite clay in a mixture of low molar mass carbonates. Similar to the fumed silica, the clay provides mechanical stability through formation of a three-dimensional network. In addition, the immobile clay platelets also serve as the anion rendering the system to be a single ion conductor. Near-unity transference number is observed in this case. However, the room temperature conductivity of the clay composite is lower than the fumed silica, revealing a value of about 10−4 S/cm. The lower conductivity can be attributed to the clay not being in a fully exfoliated form as evident from morphological analysis.}, number={14-16}, journal={ELECTROCHIMICA ACTA}, author={Walls, HJ and Riley, MW and Fedkiw, PS and Spontak, RJ and Baker, GL and Khan, SA}, year={2003}, month={Jun}, pages={2071–2077} } @article{wilder_hall_khan_spontak_2003, title={Effects of composition and matrix polarity on network development in organogels of poly(ethylene glycol) and dibenzylidene sorbitol}, volume={19}, ISSN={["0743-7463"]}, DOI={10.1021/la027081s}, abstractNote={Dibenzylidene sorbitol (DBS) is a low-molecular-weight organic molecule that can gel a variety of organic solvents and polymers by self-organizing into a three-dimensional nanofibrillar network through hydrogen-bonding and phenyl interactions. In this work, we investigate the composition dependence of such “organogels” prepared with poly(ethylene glycol) (PEG) and two PEG derivatives differing in methoxy end- group substitution, which serves to reduce matrix polarity. Transmission electron microscopy reveals that individual DBS nanofibrils measure from about 10 to 70 nm in diameter, with a primary nanofibrillar diameter of about 10 nm. Dynamic rheological measurements indicate that the rate by which the elastic modulus increases during gelation, the temperatures corresponding to gel formation and dissolution, and the magnitude of the elastic modulus are all sensitive to the DBS mass concentration (φ) and the matrix polarity. Hydroxy-end-capped PEG/DBS systems gel more slowly, but dissolve faster, than the...}, number={15}, journal={LANGMUIR}, author={Wilder, EA and Hall, CK and Khan, SA and Spontak, RJ}, year={2003}, month={Jul}, pages={6004–6013} } @article{walls_fedkiw_zawodzinski_khan_2003, title={Ion transport in silica nanocomposite electrolytes}, volume={150}, ISSN={["1945-7111"]}, DOI={10.1149/1.1544635}, abstractNote={The ion-transport properties of composite electrolytes composed of oligomers of poly(ethylene glycol) dimethyl ether, hydrophobic fumed silica, and Li(CF 3 SO 2 ) 2 N (LiTFSI) are investigated using nuclear magnetic resonance (NMR), electrophoretic NMR (ENMR), ac impedance spectroscopy, and rheology. The effects of fumed silica and salt concentration on ionic conductivity, diffusivity of ions and oligomers, and lithium transference number (T) are examined at 30°C. The fumed silica forms a self-supporting network with large pores such that the network, regardless of silica concentration, has little effect on ion-transport characteristics. Examination of the effect of salt on ion transport reveals a maximum ionic conductivity at around 1.06 M, which is attributed to a tradeoff of adding more charge carriers balanced against increased ion-ion interactions and reduced mobilities. T 1,i with respect to salt concentration surprisingly passes through a minimum around 0.35 M. The increase in T at higher concentrations is attributed to the mobilities of cations, anions, and solvating oligomer becoming constrained to the same value due to loss of free volume. The values of T Li at low salt concentrations (<0.35 M) are attributed to the ions existing in either a fully dissociated state or primarily as charged complexes. Results of T Li from ENMR and from estimation via pulse field gradient NMR (pfg-NMR) are compared showing that pfg-NMR consistently overestimates T Li . Finally, a comparison is presented of measured conductivity with that calculated from the Nernst-Einstein equation and diffusivities found from pfg-NMR measurement: we discuss possible reasons why it is inappropriate to estimate ion-pair formation by this comparison.}, number={3}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Walls, HJ and Fedkiw, PS and Zawodzinski, TA and Khan, SA}, year={2003}, month={Mar}, pages={E165–E174} } @article{riley_fedkiw_khan_2003, title={Lithium hectorite clay as the ionic conductor in LiCoO2 cathodes}, volume={150}, ISSN={["1945-7111"]}, DOI={10.1149/1.1579034}, abstractNote={Cathodes based on LiCoO 2 that contain various lithium-conducting species (lithium hectorite, lithium Laponite, and lithium-exchanged Nafion) are studied in conjunction with lithium metal anodes and composite electrolytesbased upon lithium hectorite clays as the charge carrier. Performance is compared to that of cells with a standard liquid electrolyte (i.e., LiPF 6 +1:1 w/w ethylene carbonate:ethyl methyl carbonate). Effects on cathode capacity are examined for these variables: hot-press force used in construction of the porous cathode. carbon type (graphite vs. carbon black), and clay particle size. AC impedance spectroscopy is used to probe the cells and equivalent circuits are used to model the physical processes that occur. Cathodes containing 4 wt % lithium hectorite +3 wt % lithium-exchanged Nation +3 wt % carbon black exhibit discharge capacities approximately 90 mAh/g LiCoO 2 compared to that observed in a standard cell of 110 mAh/g LiCoO 2 . These clay-containing cathodes are potentially attractive for use in single-ion conducting lithium-ion batteries designed for high discharge applications.}, number={7}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Riley, MW and Fedkiw, PS and Khan, SA}, year={2003}, month={Jul}, pages={A933–A941} } @article{abdala_tonelli_khan_2003, title={Modulation of hydrophobic interactions in associative polymers using inclusion compounds and surfactants}, volume={36}, ISSN={["1520-5835"]}, DOI={10.1021/ma034173v}, abstractNote={We report the modulation of the solution rheology of a comblike, hydrobhobically modified alkali-soluble emulsion (HASE) associative polymer through addition of α- and β-cyclodextrins (CDs). The ring-shaped CDs with hydrophobic inner cores interact with the pendant macromonomer segments of the associative polymer containing hydrophobic end groups, leading to reduction in polymer solution viscosity and dynamic moduli by several orders of magnitude. We find no interactions between the CDs and the polymer backbone as substantiated by the fact that an analogous parent polymer without hydrophobes reveals no changes in the solution rheology in the presence of CDs. In contrast, the CDs encapsulate the hydrophobic groups on the associative polymer. This is confirmed by the complexation between the CD and a surfactant modified to resemble the hydrophobic macromonomer of the associative polymer as observed using 1H NMR, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). The stoichiomet...}, number={20}, journal={MACROMOLECULES}, author={Abdala, AA and Tonelli, AE and Khan, SA}, year={2003}, month={Oct}, pages={7833–7841} } @article{walls_riley_singhal_spontak_fedkiw_khan_2003, title={Nanocomposite electrolytes with fumed silica and hectorite clay networks: Passive versus active fillers}, volume={13}, ISSN={["1616-301X"]}, DOI={10.1002/adfm.200304333}, abstractNote={Abstract}, number={9}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Walls, HJ and Riley, MW and Singhal, RR and Spontak, RJ and Fedkiw, PS and Khan, SA}, year={2003}, month={Sep}, pages={710–717} } @article{abdala_olesen_khan_2003, title={Solution rheology of hydrophobically modified associative polymers: Solvent quality and hydrophobic interactions}, volume={47}, number={2}, journal={Journal of Rheology (New York, N.Y.)}, author={Abdala, A. A. and Olesen, K. and Khan, S. A.}, year={2003}, month={Mar}, pages={497–511} } @article{walls_caines_sanchez_khan_2003, title={Yield stress and wall slip phenomena in colloidal silica gels}, volume={47}, number={4}, journal={Journal of Rheology (New York, N.Y.)}, author={Walls, H. J. and Caines, S. B. and Sanchez, A. M. and Khan, S. A.}, year={2003}, month={Jul}, pages={847–868} } @misc{kelly_khan_leduc_tayal_prud'homme_2002, title={Compositions for fracturing subterranean formations}, volume={6,428,995}, number={2002 Aug. 6}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Kelly, R. M. and Khan, S. A. and Leduc, P. and Tayal, A. and Prud'homme, R. K.}, year={2002} } @article{mccormick_hall_khan_2002, title={Entanglement relaxation and release in hard chain fluids during molecular dynamics simulations}, volume={35}, ISSN={["1520-5835"]}, DOI={10.1021/ma011134f}, abstractNote={Discontinuous molecular dynamics simulations are performed on systems containing 32 hard chains of length 192 at three volume fractions, φ = 0.40, 0.45, and 0.50, to investigate entanglement relaxation and release in model polymer melts. The relaxation behavior of the systems is compared to that predicted by the tube model and to that suggested for the release of interchain entanglements, or knots. The mean squared displacement of the chain center of mass, the mean squared displacements of inner, outer, and intermediate segments along the chain, the end-to-end vector autocorrelation function, and the apparent self-diffusion coefficient are calculated over the course of the simulations. The three relaxation times (τe, τR, and τd) predicted by the tube model are estimated in order to determine the extent to which the results exhibit tube confinement. The initial relaxation of chain segments occurs from the ends toward the middle as the tube model predicts. However, different methods for predicting the longe...}, number={15}, journal={MACROMOLECULES}, author={McCormick, JA and Hall, CK and Khan, SA}, year={2002}, month={Jul}, pages={6005–6019} } @article{pai_srinivasarao_khan_2002, title={Evolution of microstructure and rheology in mixed polysaccharide systems}, volume={35}, ISSN={["1520-5835"]}, DOI={10.1021/ma0115545}, abstractNote={Synergistic biopolymer blends composed of xanthan and enzymatically modified guar galactomannan are investigated in terms of their time-dependent properties. In particular, a side-chain cleaving enzyme, α-galactosidase, is used to cleave off galactose sugar units from guar to produce modified galactomannans with varying galactose contents of 25.2 and 16.2%. Laser scanning confocal microscopy and dynamic rheology are used to monitor the properties of each of these two modified guar gum in solution as well as in blends with xanthan as they are allowed to age over a period of 3 weeks. Our results indicate that solutions of guar with a higher galactose (25.2%) content undergo no rheological change over the period of observation and show a constant gel elastic modulus (G‘) in blends with xanthan. Confocal images of the solutions and the blends also indicate that the systems are stable over a period of 3 weeks. In contrast, guar gum with a lower galactose content (16.2%) forms interchain associations in solutio...}, number={5}, journal={MACROMOLECULES}, author={Pai, V and Srinivasarao, M and Khan, SA}, year={2002}, month={Feb}, pages={1699–1707} } @article{pai_khan_2002, title={Gelation and rheology of xanthan/enzyme-modified guar blends}, volume={49}, ISSN={["0144-8617"]}, DOI={10.1016/S0144-8617(01)00328-9}, abstractNote={The rheological behavior and synergistic character of mixed polysaccharide systems are examined for blends of xanthan with enzymatically-modified guar. In particular, the enzyme α-galactosidase is used to selectively cleave off the galactose side chains of guar in order to obtain galactomannans with tailored molecular architecture: EMG1 with a relatively high galactose content of 33.6% and a mannose (M) to galactose (G) ratio of 1.85, and EMG2 with a lower galactose content (25.2%) and an M/G ratio of 2.86. Blends of xanthan with enzymatically-modified guar gum samples are examined in terms of their dynamic rheological properties and compared to those of xanthan — locust bean gum blends. The extent of synergism, illustrated by the gel elastic modulus G′ and yield stress τc, is found to increase with increasing extent of enzymatic modification. At constant ionic strength, the EMG2 and locust bean blends behave similarly, with increasing extent of synergy as the temperature of mixing is increased. Additionally, at a fixed mixing temperature, the blends made in water have a higher elastic modulus than those made in salt. In contrast, the EMG1 blends are weaker and the dynamic moduli are unaffected by changes in the mixing temperature or ionic strength. These results are consistent with those of other researchers and are directly related to both the level of disorder in the xanthan molecule as well as the galactose content and fine structure of the galactomannan.}, number={2}, journal={CARBOHYDRATE POLYMERS}, author={Pai, VB and Khan, SA}, year={2002}, month={Aug}, pages={207–216} } @article{siripurapu_gay_royer_desimone_spontak_khan_2002, title={Generation of microcellular foams of PVDF and its blends using supercritical carbon dioxide in a continuous process}, volume={43}, ISSN={["1873-2291"]}, DOI={10.1016/S0032-3861(02)00407-X}, abstractNote={Use of supercritical carbon dioxide (scCO2) as a blowing agent to generate microcellular polymer foams (MPFs) has recently received considerable attention due to environmental concerns associated with conventional organic blowing agents. While such foams derived from amorphous thermoplastics have been previously realized, semicrystalline MPFs have not yet been produced in a continuous scCO2 process. This work describes the foaming of highly crystalline poly(vinylidene fluoride) (PVDF) and its blends with amorphous polymers during extrusion. Foams composed of neat PVDF and immiscible blends of PVDF with polystyrene exhibit poor cell characteristics, whereas miscible blends of PVDF with poly(methyl methacrylate) (PMMA) yield foams possessing vastly improved morphologies. The results reported herein illustrate the effects of blend composition and scCO2 solubility on PVDF/PMMA melt viscosity, which decreases markedly with increasing PMMA content and scCO2 concentration. Morphological characterization of microcellular PVDF/PMMA foams reveals that the cell density increases as the PMMA fraction is increased and the foaming temperature is decreased. This study confirms that novel MPFs derived continuously from semicrystalline polymers in the presence of scCO2 can be achieved through judicious polymer blending.}, number={20}, journal={POLYMER}, author={Siripurapu, S and Gay, YJ and Royer, JR and DeSimone, JM and Spontak, RJ and Khan, SA}, year={2002}, month={Sep}, pages={5511–5520} } @article{english_laurer_spontak_khan_2002, title={Hydrophobically modified associative polymer solutions: Rheology and microstructure in the presence of nonionic surfactants}, volume={41}, ISSN={["0888-5885"]}, DOI={10.1021/ie020409s}, abstractNote={We report on the rheology and morphology of a hydrophobically modified alkali-swellable emulsion (HASE) polymer solubilized in alkaline media containing nonionic surfactants. The HASE polymer consists of complex alkylaryl hydrophobes composed of oligomeric nonylphenol condensates attached to a poly(ethyl acrylate-co-methacrylic acid) backbone. The complex linear viscoelastic response of the polymer in alkaline solution suggests an unentangled network with an appreciable fraction of microgel. The concentration and hydrophile−lipophile balance (HLB) of nonionic surfactants profoundly affect the solution rheology. A surfactant of high HLB inhibits the dynamic network connectivity of the HASE polymer, as demonstrated by reductions of both the steady-shear viscosity and the dynamic storage modulus. The shear-induced structuring previously reported for this polymer is also progressively diminished as the surfactant concentration is increased. In contrast, the addition of a low-HLB surfactant promotes system structuring, as evidenced by (i) increases in the shear viscosity and the high-frequency plateau modulus and (ii) retention of the ability to undergo shear-induced structuring. We also employ cryofracture-replication transmission electron microscopy for the first time with regard to HASE associative polymers to examine the morphological characteristics of selected systems. The morphology of the HASE polymer in both latex and solubilized form appears more complex than previously anticipated, and a reasonable interpretation of these new data is provided.}, number={25}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={English, RJ and Laurer, JH and Spontak, RJ and Khan, SA}, year={2002}, month={Dec}, pages={6425–6435} } @article{zhou_fedkiw_khan_2002, title={Interfacial stability between lithium and fumed silica-based composite electrolytes}, volume={149}, ISSN={["0013-4651"]}, DOI={10.1149/1.1496483}, abstractNote={Composite electrolytes consisting of methyl-capped poly(ethylene glycol) oligomer (Mw 250), lithium bis(trifluoromethylsulfonyl)imide (Li:O = 1:20), and fumed silica were investigated. In particular, the effects of fumed silica-surface chemistry and weight percentage in the composite on cycling behavior of Li/electrolyte/Li, Li(Ni)/electrolyte/Li, and Li/electrolyte/metal oxide cells were studied. Four types of fumed silieas with various surface groups were employed, A200 (native hydroxyl groups), R805 (octyl-modified), R974 (methyl-modified), and FS-EG3 (ethylene oxide-modifed). The presence of fumed silica enhances lithium cyclability by reducing the interfacial resistance and cell-capacity fading, regardless of surface chemistry. However, the extent of the enhancing effect of fumed silica strongly depends on its surface chemistry, with the largest effect seen with A200 and the least effect seen with FS-EG3. Increasing fumed silica weight fraction intensifies the stabilizing effect.}, number={9}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Zhou, J and Fedkiw, PS and Khan, SA}, year={2002}, month={Sep}, pages={A1121–A1126} } @article{li_fedkiw_khan_2002, title={Lithium/V6O13 cells using silica nanoparticle-based composite electrolyte}, volume={47}, ISSN={["1873-3859"]}, DOI={10.1016/S0013-4686(02)00326-2}, abstractNote={The electrochemical behavior of Li/V6O13 cells is investigated at room temperature (22 °C) both in liquid electrolyte consisting of oligomeric poly(ethyleneglycol)dimethylether+lithium bis(trifluoromethylsulfonylimide) and composite electrolytes formed by blending the liquid electrolyte with silica nanoparticles (fumed silica). The addition of fumed silica yields a gel-like electrolyte that demonstrates the desirable property of suppressing lithium dendrite growth due to the rigidity and immobility of the electrolyte structure. The lithium/electrolyte interfacial resistance for composite gel electrolytes is less than that for the corresponding base-liquid electrolyte, and the charge–discharge cycle performance and electrochemical efficiency for the Li/V6O13 cell is significantly improved. The effect of fumed silica surface group on the electrochemical performance is discussed; the native hydrophilic silanol surface group appears better than fumed silica that is modified with a hydrophobic octyl surface moiety.}, number={24}, journal={ELECTROCHIMICA ACTA}, author={Li, YX and Fedkiw, PS and Khan, SA}, year={2002}, month={Sep}, pages={3853–3861} } @misc{desimone_khan_royer_spontak_walker_2002, title={Method of making foamed materialsUSing surfactants and carbon dioxide}, volume={6,403,663}, number={2002 Jun. 11}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={DeSimone, J. M. and Khan, S. A. and Royer, J. R. and Spontak, R. J. and Walker, T. A.}, year={2002} } @article{royer_gay_adam_desimone_khan_2002, title={Polymer melt rheology with high-pressure CO2 using a novel magnetically levitated sphere rheometer}, volume={43}, ISSN={["0032-3861"]}, DOI={10.1016/S0032-3861(01)00804-7}, abstractNote={A magnetically levitated sphere rheometer (MLSR) designed to measure viscosity of fluids exposed to high-pressure carbon dioxide has been developed. This device consists of a magnetic sphere submerged inside a test fluid within a high-pressure housing and levitated at a fixed point. The housing is constructed from an optically transparent sapphire tube. The cylindrical tube can be moved vertically to generate a shear flow around the levitated sphere. The difference in magnetic force required to levitate the sphere at rest and under fluid motion can be directly related to fluid viscosity. Rheological properties, specifically zero shear viscosities, of transparent high-pressure materials can be measured to a precision of about 5% and over a wide range of viscosities. In addition, operation at constant pressure, in concentration regimes from a pure polymer to an equilibrated polymer/supercritical fluid solution, and at shear rates over several orders of magnitude is possible, eliminating many of the disadvantages associated with other high-pressure rheometers. Experiments performed at different temperatures with a poly(dimethylsiloxane) melt at atmospheric pressure are compared with data from a commercial Couette rheometer to demonstrate device sensitivity and viability. Measurements of a PDMS melt plasticized by high-pressure CO2 are performed to illustrate the utility of the new rheometer under high-pressure conditions. Experimental data are obtained at 30 °C, for pressures up to 20.7 MPa and CO2 concentrations reaching 30 wt%. Viscosity reductions of nearly two orders of magnitude compared with the pure polymer viscosity at atmospheric pressure are observed. Additionally, the effects of pressure on a polymer/CO2 system are directly investigated taking advantage of the constant pressure operation mode of the MLSR. This allows us, for the first time in experiments of polymers with supercritical fluids, to decouple the effects of CO2 concentration and pressure in a single device.}, number={8}, journal={POLYMER}, author={Royer, JR and Gay, YJ and Adam, M and DeSimone, JM and Khan, SA}, year={2002}, month={Apr}, pages={2375–2383} } @article{andrady_nunez_chiou_khan_2002, title={Rheology of concentrated solutions of hyperbranched polyesters}, volume={42}, ISSN={0032-3888 1548-2634}, url={http://dx.doi.org/10.1002/pen.11097}, DOI={10.1002/pen.11097}, abstractNote={Abstract}, number={11}, journal={Polymer Engineering & Science}, publisher={Wiley}, author={Andrady, Anthony L. and Nunez, Carlos M. and Chiou, Bor-Sen and Khan, Saad A.}, year={2002}, month={Nov}, pages={2065–2071} } @article{burke_ha_pysz_khan_2002, title={Rheology of protein gels synthesized through a combined enzymatic and heat treatment method}, volume={31}, ISSN={["0141-8130"]}, DOI={10.1016/S0141-8130(02)00043-0}, abstractNote={Whey protein gels prepared under acidic conditions (pH<4.6) remain largely unutilized because of their weak and brittle nature in contrast to the favorable elastic gels produced at neutral or basic conditions. However, such usage is important, as low pH food products are desirable due to their shelf stability and less stringent sterilization processes. In this study, we use a two-step process involving enzyme followed by heat treatment to produce whey protein gels at low pH (4.0). Dynamic rheological measurements reveal that the gel elastic modulus and yield stress increase substantially when heat treatment is supplemented with enzyme treatment. Both the elastic modulus and yield stress increase with increasing enzyme concentration or treatment time. In contrast, the dynamic yield strain decreases with enzyme concentration but increases with time of enzyme treatment. These results are explained in terms of the enzyme treatment time affecting the diffusion of the enzyme within the gel. This in turn leads to two types of gel microstructure at short and long enzyme treatment times, with the extent of enzyme diffusion modulating the structure at intermediate times.}, number={1-3}, journal={INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES}, author={Burke, MD and Ha, SY and Pysz, MA and Khan, SA}, year={2002}, month={Dec}, pages={37–44} } @article{mccormick_hall_khan_2002, title={The effect of position along the chain on the dynamic properties of hard chain segments}, volume={117}, ISSN={["1089-7690"]}, DOI={10.1063/1.1483295}, abstractNote={Discontinuous molecular dynamics simulations are performed on systems containing 32 hard chains of length 192 at three volume fractions, φ=0.40, 0.45, and 0.50, to investigate the effect of position on the segmental mean squared displacement. The mean squared displacements of various sized blocks of segments at different positions along the chain are calculated. First, the effect of block size on the dynamics of end and middle blocks is considered. It is found that small blocks provide a greater difference between the mean squared displacements of middle blocks, end blocks, and the whole chain than larger equal-sized blocks. Next, the portions of the chain exhibiting end and middle behavior are determined. It is found that a large portion of the chain displays middle behavior, while a small portion displays end behavior. Finally, the dynamics of segment relaxation along the chain are studied. The relaxation of small blocks of segments at different positions along the chain starts at the chain ends and progresses toward the chain middle with time, as the tube model predicts. The minor chain length, the portion of the chain that has relaxed, follows a power law with time, but the power is somewhat less than predicted.}, number={2}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={McCormick, JA and Hall, CK and Khan, SA}, year={2002}, month={Jul}, pages={944–957} } @article{riley_fedkiw_khan_2002, title={Transport properties of lithium hectorite-based composite electrolytes}, volume={149}, ISSN={["1945-7111"]}, DOI={10.1149/1.1470652}, abstractNote={Conductivity and lithium-ion transference numbers are reported for physically gelled composite electrolytes using lithium hectorite clay as the charge carrier and carbonate solvents (ethylene carbonate, propylene carbonate, and dimethyl carbonate). Results are compared with those of typical lithium-ion battery electrolytes based on lithium hexafluorophosphate (LiPF 6 ) and carbonate solvents Room-temperature conductivities of the composite electrolytes as high as 2 × 10 4 S/cm were measured. Because of the nature of the anionic clay particulates creating the gel structure, near-unity lithium-ion transference numbers are expected and were observed as high as 0.98, as measured by the de polarization method using lithium-metal electrodes. Since the carbonates react with lithium and create mobile ionic species that significantly reduce the observed lithium-ion transference number care must be taken to minimize or eliminate the presence of the reaction-formed ionic species. These hectorite-based composite systems are possible electrolytes for rechargeable lithium-ion batteries requiring high discharge rates.}, number={6}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Riley, M and Fedkiw, PS and Khan, SA}, year={2002}, month={Jun}, pages={A667–A674} } @misc{kelly_khan_leduc_tayal_prud'homme_2001, title={Compositions for fracturing subterranean formations}, volume={6,197,730}, number={2001 Mar. 6}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Kelly, R. M. and Khan, S. A. and Leduc, P. and Tayal, A. and Prud'homme, R. K.}, year={2001} } @article{mercurio_khan_spontak_2001, title={Dynamic rheological behavior of DBS-induced poly(propylene glycol) physical gels}, volume={40}, ISSN={["1435-1528"]}, DOI={10.1007/s003970000119}, number={1}, journal={RHEOLOGICA ACTA}, author={Mercurio, DJ and Khan, SA and Spontak, RJ}, year={2001}, month={Jan}, pages={30–38} } @article{royer_desimone_khan_2001, title={High-pressure rheology and viscoelastic scaling predictions of polymer melts containing liquid and supercritical carbon dioxide}, volume={39}, ISSN={0887-6266 1099-0488}, url={http://dx.doi.org/10.1002/polb.10057}, DOI={10.1002/polb.10057}, abstractNote={Abstract}, number={23}, journal={Journal of Polymer Science Part B: Polymer Physics}, publisher={Wiley}, author={Royer, Joseph R. and DeSimone, Joseph M. and Khan, Saad A.}, year={2001}, pages={3055–3066} } @article{martinache_royer_siripurapu_henon_genzer_khan_carbonell_2001, title={Processing of polyamide 11 with supercritical carbon dioxide}, volume={40}, ISSN={["0888-5885"]}, DOI={10.1021/ie010410b}, abstractNote={The supercritical carbon dioxide induced swelling and plasticization of polyamide 11 were investigated. The swelling kinetics exhibit an initial region of large swelling, in which the diffusion of CO2 into the polymer follows Fickian behavior, and a subsequent region of small volume increase that asymptotically approaches an equilibrium swelling value. The diffusion coefficient of CO2 in polyamide 11 was calculated from the initial slope of the swelling kinetics data. CO2, injected up to 3 wt % using an extrusion rheometer, is shown to be an effective plasticizer for polyamide 11, lowering the viscosity of the polymer melt by as much as 50%. The use of CO2 as a blowing agent was also investigated, and we report preliminary foaming attempts using a batch process. We obtained homogeneously distributed foams, featuring well-defined closed cells with an average diameter of 30 μm that had an unfoamed skin layer.}, number={23}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Martinache, JD and Royer, JR and Siripurapu, S and Henon, FE and Genzer, J and Khan, SA and Carbonell, RG}, year={2001}, month={Nov}, pages={5570–5577} } @article{shay_raghavan_khan_2001, title={Thermoreversible gelation in aqueous dispersions of colloidal particles bearing grafted poly(ethylene oxide) chains}, volume={45}, number={4}, journal={Journal of Rheology (New York, N.Y.)}, author={Shay, J. S. and Raghavan, S. R. and Khan, S. A.}, year={2001}, month={Jul}, pages={913–927} } @article{raghavan_hou_baker_khan_2000, title={Colloidal interactions between particles with tethered nonpolar chains dispersed in polar media: Direct correlation between dynamic rheology and interaction parameters}, volume={16}, ISSN={["0743-7463"]}, DOI={10.1021/la9815953}, abstractNote={Colloidal interactions between particles dispersed in a liquid can be suitably tailored by modifying the surface chemistry of the particles. In the case of fumed silica particles, the surface can be systematically altered from hydrophilic to hydrophobic by replacing a portion of the original silanol (Si−OH) groups by nonpolar alkyl chains. In this study, we probe the effect of surface modification of fumed silica on their rheology and microstructure in polar media. Variables of interest include the length of the tethered alkyl chain and the extent of surface coverage. For the continuous phase, we examine a range of polyether liquids comprising different architectures and molecular weights. We find that when the alkyl chains are C8 or longer, and are attached at saturation levels, a dense nonpolar surface layer is formed on each silica unit. Such particles experience strong interactions in polar media, leading to the formation of a volume-filling network (gel). We show that these interactions arise as a re...}, number={3}, journal={LANGMUIR}, author={Raghavan, SR and Hou, J and Baker, GL and Khan, SA}, year={2000}, month={Feb}, pages={1066–1077} } @article{tayal_khan_2000, title={Degradation of a water-soluble polymer: Molecular weight changes and chain scission characteristics}, volume={33}, ISSN={["0024-9297"]}, DOI={10.1021/ma000736g}, abstractNote={Computer simulations in conjunction with molecular weight distributions, obtained from gel permeation chromatography (GPC), are used to obtain physical insights on the mechanisms of degradation of guar galactomannan, a naturally occuring polysaccharide. Two different modes of degradation, sonication and enzymatic hydrolysis, are compared. Both modes of guar degradation reveal similar features in terms of changes in molecular weights, a rapid reduction followed by a slow decrease. However, the molecular weight distributions are significantly different, with ultrasonication leading to a narrowing of the molecular weight distribution and enzymatic hydrolysis resulting in its broadening. Sonication of guar results in a random degradation of chains, so that all bonds have equal probability of cleavage. In contrast, enzymatic degradation does not follow any of the typical modes of chain scission (random, Gaussian, and central), indicating that enzymatic hydrolysis of guar does not obey a “single scission” pathw...}, number={26}, journal={MACROMOLECULES}, author={Tayal, A and Khan, SA}, year={2000}, month={Dec}, pages={9488–9493} } @article{burke_park_srinivasarao_khan_2000, title={Diffusion of macromolecules in polymer solutions and gels: A laser scanning confocal microscopy study}, volume={33}, ISSN={["1520-5835"]}, DOI={10.1021/ma000786l}, abstractNote={Laser scanning confocal microscopy combined with fluorescence recovery after photobleaching is an effective tool to measure the diffusion coefficients of macromolecules in cross-linked hydrogels and polymer solutions. In this study, the effects of enzyme treatment on the diffusion of macromolecules (FITC-dextran) in guar solutions and titanium-guar hydrogels are examined. Enzyme treatment with β-mannanase, a polymer backbone cleaving enzyme, quickly increases the diffusion coefficient of the probe molecules in both solutions and hydrogels to that in water. Enzyme treatment of guar solutions and hydrogels with α-galactosidase, a side chain cleaving enzyme, displays a unique behavior due to changes in the fine structure of guar. The removal of galactose branches from the mannan backbone of guar creates additional hyperentanglements (i.e., cross-links), which reduce the water holding capacity of guar and induce syneresis. If the depth at which the diffusion coefficient is measured remains constant, a minimum...}, number={20}, journal={MACROMOLECULES}, author={Burke, MD and Park, JO and Srinivasarao, M and Khan, SA}, year={2000}, month={Oct}, pages={7500–7507} } @article{shay_english_spontak_balik_khan_2000, title={Dispersion polymerization of polystyrene latex stabilized with novel grafted poly(ethylene glycol) macromers in 1-propanol/water}, volume={33}, ISSN={["0024-9297"]}, DOI={10.1021/ma992152o}, abstractNote={A novel hydrophilic macromer adapted for chemical grafting has been synthesized. It consists of methyl-end-capped poly(ethylene glycol) functionalized with a urethane terminus. Dispersion polymerization of styrene in an alcohol/water medium in the presence of the macromer allows chemical grafting of the macromer to the surfaces of the developing polystyrene (PS) latex particles. Scanning and transmission electron microscopies confirm the formation of spherical, submicron polystyrene particles. Transmission electron microscopy of films prepared from the latex particles also permits direct visualization of the stabilizing macromer layer grafted on the PS particle surfaces. Data acquired from proton nuclear magnetic resonance reveal a direct correlation between the concentration of macromer in the reaction mixture and the amount grafted to the latex particles. Rheological techniques are employed to (i) discern the stabilization efficacy of the macromer and (ii) identify correlations between latex and flow ch...}, number={18}, journal={MACROMOLECULES}, author={Shay, JS and English, RJ and Spontak, RJ and Balik, CM and Khan, SA}, year={2000}, month={Sep}, pages={6664–6671} } @article{walls_zhou_yerian_fedkiw_khan_stowe_baker_2000, title={Fumed silica-based composite polymer electrolytes: synthesis, rheology, and electrochemistry}, volume={89}, ISSN={["0378-7753"]}, DOI={10.1016/S0378-7753(00)00424-9}, abstractNote={An overview of our research is presented on developing composite polymer electrolytes (CPEs) based on low-molecular weight polyethylene oxide (PEO) (namely, poly(ethylene glycol) dimethyl ether), lithium salts (e.g. lithium triflate, lithium imide, etc.), and fumed silica. These CPEs demonstrate high room-temperature conductivites (>10−3 S/cm), mechanical strength, and form stable interfaces with lithium metal as a result of the fumed silica. The surface groups on the fumed silica determine the mechanical properties of the CPE while the low-molecular weight PEO and lithium salt determine the ionic transport properties. These CPEs show promise as electrolytes for the next generation of rechargeable lithium batteries.}, number={2}, journal={JOURNAL OF POWER SOURCES}, author={Walls, HJ and Zhou, J and Yerian, JA and Fedkiw, PS and Khan, SA and Stowe, MK and Baker, GL}, year={2000}, month={Aug}, pages={156–162} } @article{royer_gay_desimone_khan_2000, title={High-pressure rheology of polystyrene melts plasticized with CO2: Experimental measurement and predictive scaling relationships}, volume={38}, number={23}, journal={Journal of Polymer Science. Part B, Polymer Physics}, author={Royer, J. R. and Gay, Y. J. and Desimone, J. M. and Khan, S. A.}, year={2000}, month={Dec}, pages={3168–3180} } @article{shay_english_khan_2000, title={Rheological behavior of a polymerically stabilized latex for use in water-borne coatings}, volume={40}, ISSN={["0032-3888"]}, DOI={10.1002/pen.11276}, abstractNote={Abstract}, number={6}, journal={POLYMER ENGINEERING AND SCIENCE}, author={Shay, JS and English, RJ and Khan, SA}, year={2000}, month={Jun}, pages={1469–1479} } @article{raghavan_walls_khan_2000, title={Rheology of silica dispersions in organic liquids: New evidence for solvation forces dictated by hydrogen bonding}, volume={16}, ISSN={["0743-7463"]}, DOI={10.1021/la991548q}, abstractNote={Dispersions of hydrophilic fumed silica are investigated in a range of polar organic media. The silica forms stable, low-viscosity sols exhibiting shear thickening behavior in a host of liquids, including ethylene glycol and its oligomers and short-chain alcohols, such as n-propanol. In contrast, the silica flocculates into colloidal gels in other liquids, such as glycols with methyl end-caps and longer-chain alcohols. We suggest that there is a causal relationship between the hydrogen-bonding ability of the liquid and the colloidal microstructure observed. In strongly hydrogen-bonding liquids, a solvation layer is envisioned to form on the silica surface through hydrogen bonding between liquid molecules and surface silanol groups (Si−OH). This gives rise to short-range, non-DLVO repulsions (“solvation forces”) which stabilize the silica particles. In contrast, in the case of liquids with limited hydrogen-bonding ability, silanols on adjacent silica particles are envisioned to interact directly by hydroge...}, number={21}, journal={LANGMUIR}, author={Raghavan, SR and Walls, HJ and Khan, SA}, year={2000}, month={Oct}, pages={7920–7930} } @article{nunez_chiou_andrady_khan_2000, title={Solution Rheology of Hyperbranched Polyesters and Their Blends with Linear Polymers}, volume={33}, ISSN={0024-9297 1520-5835}, url={http://dx.doi.org/10.1021/ma991044z}, DOI={10.1021/ma991044z}, abstractNote={The rheological properties of different generations of hyperbranched polyesters in 1-methyl-2-pyrrolidinone solvent and their blends with a poly(2-hydroxyethyl methacrylate) are examined in this study. All the hyperbranched polyester solutions exhibit Newtonian behavior, with steady shear viscosities independent of shear rate. This indicates the absence of physical entanglements in these systems. In addition, solution viscosities are found to be only slightly affected by the different generations of the hyperbranched polymer. The polyesters have very small intrinsic viscosities, and their hydrodynamic radius scales as Rh ∼ M0.39, suggesting a less packed structure than dendrimers. All generations of the hyperbranched polyesters also show comparable apparent activation energies of flow over the temperature range studied. Replacing linear polymers with hyperbranched polymers causes large reductions in the blend viscosities. This behavior can be attributed to the decrease in both the number of physical entan...}, number={5}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Nunez, Carlos M. and Chiou, Bor-Sen and Andrady, Anthony L. and Khan, Saad A.}, year={2000}, month={Mar}, pages={1720–1726} } @article{mccormick_royer_hwang_khan_2000, title={Tailored rheology of a metallocene polyolefin through silane crafting and subsequent silane crosslinking}, volume={38}, DOI={10.1002/1099-0488(20000915)38:18<2468::AID-POLB140>3.0.CO;2-7}, abstractNote={Polymer modification through silane grafting and its subsequent crosslinking allows the rheological properties of a polymer to be tuned from those of a viscous melt to those of a crosslinked elastic network. In this study, a metallocene polyolefin resin is grafted with vinyl trimethoxy silane (VTMS) using dicumyl peroxide (DCP) as the initiator and is subsequently crosslinked in an oxidative environment. Dynamic rheological experiments are conducted to elucidate the effects of DCP and VTMS concentrations on the grafting and ensuing crosslinking processes. We find that the addition of VTMS alone to the polymer produces no grafting. In contrast, the presence of DCP by itself leads to direct crosslinking between polymer chains as suggested by an increase in elastic modulus and complex viscosity. Samples containing both DCP and VTMS undergo silane grafting, with the extent of grafting increasing with increasing DCP concentration. This conclusion is borne out by both rheological and Fourier transform infrared measurements. The grafted samples undergo silane crosslinking only in an oxidative environment and at temperatures equal to or greater than 190 °C. During crosslinking, the samples undergo a transition from a viscous melt with frequency-dependent moduli to a gel exhibiting frequency-independent moduli with the elastic modulus exceeding the viscous modulus. However, the kinetics of crosslinking and the extent of the modulus increase are a function of the DCP concentration, with both exhibiting a maximum at a specific DCP and VTMS combination.}, number={18}, journal={Journal of Polymer Science. Part B, Polymer Physics}, author={McCormick, J. A. and Royer, J. R. and Hwang, C. R. and Khan, Saad}, year={2000}, pages={2468–2479} } @article{kenkare_hall_khan_2000, title={Theory and simulation of the swelling of polymer gels}, volume={113}, ISSN={["0021-9606"]}, DOI={10.1063/1.481806}, abstractNote={A combined discontinuous molecular dynamics and Monte Carlo simulation technique is used to study the swelling of athermal, continuous-space, near-perfect, trifunctional polymer networks containing hard chains of lengths 20 and 35 immersed in an athermal hard-sphere solvent. The swelling simulations are conducted under conditions of constant pressure and chemical potential. A simple, analytical theory for gel swelling is presented in which the gel free energy is calculated as the sum of an elastic, affine-type term, and a liquidlike mixing term that is based on the generalized-Flory dimer equation of state. The theory shows good agreement with our simulation results for the gel properties at swelling equilibrium.}, number={1}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Kenkare, NR and Hall, CK and Khan, SA}, year={2000}, month={Jul}, pages={404–418} } @article{burke_khan_2000, title={Triggered enzymatic degradation of a water-soluble polymer solution using a novel inhibitor}, volume={1}, ISSN={["1526-4602"]}, DOI={10.1021/bm000051o}, abstractNote={Controlled enzymatic degradation of solutions of guar galactomannan, a naturally occurring polysaccharide, offers a powerful tool to enhance its usage in a variety of applications. In this study, we use viscometry to investigate the use of tris(hydroxymethyl)aminomethane (Tris) as a reversible, pH-dependent inhibitor to control the degradation of guar galactomannan by Aspergillus niger beta-mannanase. Viscosity measurements of pH 9 guar solutions containing 25 mM Tris show no reduction in the viscosity when treated with beta-mannanase. In contrast, samples containing no Tris show significant reduction in viscosity within an hour. Samples maintained at a pH of 9 in the presence of Tris for several hours show no change in viscosity; however, reduction of the pH of the sample to 4 initiates enzymatic degradation of the guar solution resulting in a rapid reduction in solution viscosity. This reversible, pH-dependent inhibition is possibly a result of the protonation state of Tris as well as key amino acids in the active site.}, number={4}, journal={BIOMACROMOLECULES}, author={Burke, MD and Khan, SA}, year={2000}, pages={688–695} } @article{english_raghavan_jenkins_khan_1999, title={Associative polymers bearing n-alkyl hydrophobes: rheological evidence for microgel-like behavior}, volume={43}, number={5}, journal={Journal of Rheology (New York, N.Y.)}, author={English, R. J. and Raghavan, S. R. and Jenkins, R. D. and Khan, S. A.}, year={1999}, month={Sep}, pages={1175–1194} } @article{royer_desimone_khan_1999, title={Carbon dioxide-induced swelling of poly( dimethylsiloxane)}, volume={32}, ISSN={["0024-9297"]}, DOI={10.1021/ma9904518}, abstractNote={A new experimental device is used to monitor in situ the swelling behavior of poly(dimethylsiloxane) melts in contact with supercritical carbon dioxide. The effects of pressure, temperature, and sample molecular weight on the kinetics and extent of swelling are examined using this experimental technique. The swelling kinetics of all polymer samples exhibit two distinct regimes:  an initial region of large swelling in which the diffusion of CO2 into the polymer follow Fickian behavior and a subsequent region of small volume increase asymptotic to an equilibrium swelling value. Diffusion coefficients of CO2, obtained from the initial swelling kinetics data, are found to be relatively insensitive to pressure, increase with temperature, and decrease with polymer molecular weight with the latter exhibiting a power-law dependence with an exponent of ∼−2. The extent of swelling increases with both pressure and molecular weight but exhibits different trends with temperature depending on system pressure. For press...}, number={26}, journal={MACROMOLECULES}, author={Royer, JR and DeSimone, JM and Khan, SA}, year={1999}, month={Dec}, pages={8965–8973} } @misc{khan_fedkiw_baker_fan_raghavan_hou_1999, title={Composite electrolyte containing surface modified fumed silica}, volume={5,965,299}, number={1999 Oct. 12}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Khan, S. A. and Fedkiw, P. S. and Baker, G. L. and Fan, J. and Raghavan, S. R. and Hou, J.}, year={1999}, month={Oct} } @misc{kelly_khan_leduc_tayal_prud'homme_1999, title={Compositions for fracturing subterranean formations}, volume={5,869,435}, number={1999 Feb. 9}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Kelly, R. M. and Khan, S. A. and Leduc, P. and Tayal, A. and Prud'homme, R. K.}, year={1999} } @article{bhatt_royer_hwang_khan_1999, title={Compressive stress relaxation of metallocene-based polyolefin foams: Effect of gamma-ray-induced crosslinking}, volume={37}, ISSN={["0887-6266"]}, DOI={10.1002/(SICI)1099-0488(19990601)37:11<1045::AID-POLB1>3.3.CO;2-0}, abstractNote={Journal of Polymer Science Part B: Polymer PhysicsVolume 37, Issue 11 p. 1045-1056 Article Compressive stress relaxation of metallocene-based polyolefin foams: Effect of gamma-ray-induced crosslinking Chinmay U. Bhatt, Chinmay U. Bhatt Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this authorJoseph R. Royer, Joseph R. Royer Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this authorC. Robin Hwang, C. Robin Hwang Becton Dickinson Technologies, 21 Davis Drive, RTP, North Carolina 27709-2016Search for more papers by this authorSaad A. Khan, Corresponding Author Saad A. Khan Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this author Chinmay U. Bhatt, Chinmay U. Bhatt Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this authorJoseph R. Royer, Joseph R. Royer Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this authorC. Robin Hwang, C. Robin Hwang Becton Dickinson Technologies, 21 Davis Drive, RTP, North Carolina 27709-2016Search for more papers by this authorSaad A. Khan, Corresponding Author Saad A. Khan Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this author First published: 02 April 1999 https://doi.org/10.1002/(SICI)1099-0488(19990601)37:11<1045::AID-POLB1>3.0.CO;2-9Citations: 18AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Abstract Metallocene-based polyolefin (MPO) foams possess a closed-cell structure which is in contrast to the open-celled structure of polyurethane (PU) foams. In this study, we investigate the effects of gamma-irradiation on the mechanical behavior of MPO foams using PU foam behavior as a basis. Compressive step-strain experiments reveal a two-step relaxation process in MPO foams, dominated by polymer chain relaxation at short times and gas diffusion from the closed cells at longer times. On the other hand, the relaxation in PU foams is similar to fully crosslinked polymers with the relaxation modulus reaching an equilibrium value after an initial decay. The closed-celled structure of MPO foams lends to rapid stress relaxation and low structural recoverability upon application of compressive loads. Exposure to gamma radiation induces crosslinking in MPO foams and improves their resilience and recoverability. Stress relaxation tests reveal that nonradiated MPO foams show complete relaxation and structural loss at high temperatures. In contrast, radiated MPO foams show a significant retardation in relaxation kinetics and structural stability attributed to radiation-induced crosslinking. Dynamic rheology and solvent-extraction studies also support the results obtained from stress-relaxation experiments. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1045–1056, 1999 Citing Literature Volume37, Issue111 June 1999Pages 1045-1056 RelatedInformation}, number={11}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Bhatt, CU and Royer, JR and Hwang, CR and Khan, SA}, year={1999}, month={Jun}, pages={1045–1056} } @article{walker_raghavan_royer_smith_wignall_melnichenko_khan_spontak_1999, title={Enhanced miscibility of low-molecular-weight polystyrene polyisoprene blends in supercritical CO2}, volume={103}, ISSN={["1089-5647"]}, DOI={10.1021/jp990551f}, abstractNote={While ongoing efforts continue to explore the high-pressure phase equilibria of polymer blends, few studies have attempted to address the impact of a supercritical (sc) fluid on such equilibria. In this work, we report on the phase behavior of an upper critical solution temperature (UCST) polymer blend in the presence of supercritical carbon dioxide (scCO2), a nonselective plasticizing agent. Blends composed of low-molecular-weight polystyrene and polyisoprene have been examined as a function of temperature in scCO2 by visual inspection, small-angle neutron scattering, and spectrophotometry. In the presence of scCO2, the cloud point temperature is depressed by as much as 28 °C, depending on both blend composition and CO2 pressure. Complementary studies performed with nitrogen decouple the plasticization efficacy of CO2 from free-volume compression due to hydrostatic pressure. Existence of a pressure yielding a maximum in CO2-induced cloud point depression is established. These results provide evidence for...}, number={26}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Walker, TA and Raghavan, SR and Royer, JR and Smith, SD and Wignall, GD and Melnichenko, Y and Khan, SA and Spontak, RJ}, year={1999}, month={Jul}, pages={5472–5476} } @article{ryu_gilbert_khan_1999, title={Influence of cationic additives on the rheological, optical, and printing properties of ink-jet coatings}, volume={82}, number={11}, journal={TAPPI Journal}, author={Ryu, R. Y. and Gilbert, R. D. and Khan, S. A.}, year={1999}, month={Nov}, pages={128–134} } @misc{spontak_roberts_prevysh_khan_1999, title={Method of reducing the viscosity of a black liquor using thiocyanate salt}, volume={5,900,112}, number={1999 May 4}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Spontak, R. J. and Roberts, J. E. and Prevysh, V. A. and Khan, S. A.}, year={1999} } @article{laurer_khan_spontak_satkowski_grothaus_smith_lin_1999, title={Morphology and rheology of SIS and SEPS triblock copolymers in the presence of a midblock-selective solvent}, volume={15}, ISSN={["0743-7463"]}, DOI={10.1021/la981441n}, abstractNote={While numerous fundamental studies have sought to elucidate the effect of a parent homopolymer on the morphological characteristics and mechanical properties of microphase-ordered block copolymer blends, few comparable efforts have extended such studies to concentrated copolymer solutions in the presence of a low-molar-mass block-selective solvent. In this work, we investigate the microstructures that form in blends of a poly(styrene-block-isoprene-block-styrene) (SIS) triblock copolymer with a midblock-selective aliphatic mineral oil. To discern the influence of midblock/oil compatibility on blend morphology and properties, identical blends with a poly[styrene-block-(ethylene-alt-propylene)-block-styrene] (SEPS) copolymer, the hydrogenated variant of the SIS copolymer, have likewise been examined. The saturated midblock of the SEPS copolymer is responsible for the observed shifts in morphology stability limits and higher dynamic elastic shear moduli relative to the SIS analogue. These results reveal that...}, number={23}, journal={LANGMUIR}, author={Laurer, JH and Khan, SA and Spontak, RJ and Satkowski, MM and Grothaus, JT and Smith, SD and Lin, JS}, year={1999}, month={Nov}, pages={7947–7955} } @article{kenkare_hall_khan_1999, title={Pressure-volume properties of endlinked hard-chain polymer networks}, volume={110}, ISSN={["0021-9606"]}, DOI={10.1063/1.478659}, abstractNote={Equilibrium molecular dynamics simulations are used to obtain the pressure and configurational chain properties of near-perfect, off-lattice, trifunctional hard-chain networks of chain lengths 20, 35, 50, and 100, and of tetrafunctional hard-chain networks of chain lengths 20, 35, and 50 over a range of packing fractions. Our simulation results show that the variation of network pressure with density is similar to that of uncrosslinked chain systems of the same chain length, except at low densities where the network pressure shows a negative region, as first observed by Escobedo and de Pablo. We present a theoretical treatment leading to an analytical expression for the network pressure as the sum of liquid-like and elastic contributions. The liquid-like contribution is obtained by extending the generalized Flory-dimer theory to networks, and the elastic contribution is obtained by treating the network as a set of interpenetrated dendrimers and using an ideal chain-spring analogy to calculate the free energy. The theoretical predictions for network pressure are in good agreement with simulation data.}, number={15}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Kenkare, NR and Hall, CK and Khan, SA}, year={1999}, month={Apr}, pages={7556–7573} } @article{tayal_pai_khan_1999, title={Rheology and microstructural changes during enzymatic degradation of a guar-borax hydrogel}, volume={32}, ISSN={["1520-5835"]}, DOI={10.1021/ma990167g}, abstractNote={Hydrogels composed of borax cross-linked guar galactomannans are enzymatically degraded using endo-β-mannanase, an enzyme which cleaves the polymer chain backbone. Dynamic rheological measurements show the elastic (G‘) and viscous (G‘ ‘) moduli to be sensitive to gel structure and to reduce significantly during the enzymatic hydrolysis process. The reduction in rheological properties shows three distinct regimes:  an initial large decrease, a slower reduction rate at intermediate times, and an accelerated reduction at longer degradation times. In contrast, the polymer chain molecular weight, obtained from gel permeation chromatography, reduces rapidly at short times and at a slower rate subsequently. We therefore find the kinetics of moduli reduction to be dictated by the relationship between gel structure and rheological properties, rather than purely the rates of chain scission. At short times, the large decrease in moduli is analogous to changes in molecular weight and can directly be attributed to cha...}, number={17}, journal={MACROMOLECULES}, author={Tayal, A and Pai, VB and Khan, SA}, year={1999}, month={Aug}, pages={5567–5574} } @article{tayal_kelly_khan_1999, title={Rheology and molecular weight changes during enzymatic degradation of a water-soluble polymer}, volume={32}, ISSN={["1520-5835"]}, DOI={10.1021/ma980773w}, abstractNote={The rheological behavior and molecular weight characteristics of a natural polymer undergoing enzymatic hydrolysis were examined for aqueous guar solutions. Changes in weight-average molecular weight (Mw), deduced from gel permeation chromatography (GPC), were used to construct a kinetic model for the process, such that 1/Mw ∝ kt, with the rate constant, k, varying inversely with polymer concentration. This relationship suggests that enzymatic degradation was zeroth-order in guar concentration. These findings contrast with previous studies of natural polymer degradation which usually have interpreted the linear relationship between 1/M and time as first-order processes. Our analysis reveals that this linear relationship is expected regardless of the reaction order and that the true order can be determined only from the dependence of the degradation rate on initial polymer concentration. Rheological properties were sensitive to extent of degradation; several orders of magnitude change in zero shear viscosi...}, number={2}, journal={MACROMOLECULES}, author={Tayal, A and Kelly, RM and Khan, SA}, year={1999}, month={Jan}, pages={294–300} } @article{raghavan_riley_fedkiw_khan_1998, title={Composite polymer electrolytes based on poly(ethylene glycol) and hydrophobic fumed silica: Dynamic rheology and microstructure}, volume={10}, ISSN={["0897-4756"]}, DOI={10.1021/cm970406j}, abstractNote={Dynamic rheological techniques are used to probe the microstructures present in fumed silica-based composite polymer electrolytes. These electrolytes are obtained by dispersing hydrophobic fumed silica in a poly(ethylene glycol)−lithium salt solution and display high conductivities (σ298K > 10-3 S/cm), mechanical stability, and easy processability. The materials behave as soft solids (gels) under ambient conditions due to the presence of a three-dimensional network of silica entities. Network formation occurs as a result of van der Waals (dispersion) forces between the nonpolar surface layers on silica units. Factors which affect the van der Waals interaction, and hence the gel network density, include the nature of the PEG end group, the presence of ionic species, and the size of the hydrophobic surface group on the silica. The composites also exhibit shear-thinning behavior due to the shear-induced disruption of network bonds, and this behavior can be advantageously utilized in electrolyte processing.}, number={1}, journal={CHEMISTRY OF MATERIALS}, author={Raghavan, SR and Riley, MW and Fedkiw, PS and Khan, SA}, year={1998}, month={Jan}, pages={244–251} } @article{fan_raghavan_yu_khan_fedkiw_hou_baker_1998, title={Composite polymer electrolytes using surface-modified fumed silicas: conductivity and rheology}, volume={111}, ISSN={["0167-2738"]}, DOI={10.1016/S0167-2738(98)00151-9}, abstractNote={We report results from our studies on composite polymer electrolytes based on novel surface-modified fumed silicas. The electrolytes were prepared by dispersing fumed silica in a matrix formed by methyl-capped polyethylene glycol and lithium salt. Silicas with widely different surface chemistries were synthesized in order to study the effects of surface modification, with the attached surface groups ranging from non-polar alkyl moieties (C1 or C8) to polar polyethylene oxide (PEO) oligomers (MW∼200). We find, rather surprisingly, that the conductivity is independent of the type of surface group present on the silica. Moreover, the conductivity decreases only slightly on addition of fumed silica, even at high weight fraction of solids. In contrast, the rheological properties of the composites are strongly affected by both the silica surface chemistry and weight fraction. Dynamic rheology measurements reveal that fumed silicas with silanol and octyl coverage both flocculate into gels (networks). The resulting materials are mechanically stable, with the elastic modulus of the gel being strongly dependent upon weight fraction of solids. The PEO-modified silica, in contrast, gives rise to a low-viscosity suspension where the silica units exist as distinct, non-interacting species. The findings of this study have significant implications for future work on composite electrolytes, in that we can tailor the mechanical properties of the system without affecting the electrochemical behavior.}, number={1-2}, journal={SOLID STATE IONICS}, author={Fan, J and Raghavan, SR and Yu, XY and Khan, SA and Fedkiw, PS and Hou, J and Baker, GL}, year={1998}, month={Aug}, pages={117–123} } @article{kenkare_smith_hall_khan_1998, title={Discontinuous molecular dynamics studies of end-linked polymer networks}, volume={31}, ISSN={["0024-9297"]}, DOI={10.1021/ma9801422}, abstractNote={Discontinuous molecular dynamics simulations are used to study the structure and relaxation of large, off-lattice, near-perfect, tri- and tetrafunctional polymer networks at a packing fraction of 0.43. The networks are constructed by end-linking freely jointed, tangent hard-sphere chains ranging in length from N = 20 to N = 150 and are then relaxed for 5−20 billion collisions. The simulation trajectories are used to calculate the radius of gyration and end-to-end distance of the network chains, the static structure factor of the cross-links, the mean-squared displacement of the cross-links and chain inner segments, the intermediate scattering function of the chains, and the elastic modulus of the network. The structure and properties of the networks are shown to depend heavily on the manner in which the network is initially constructed. The dynamics of the network cross-links and chain inner segments are similar to those of melt chains at short times and show evidence of spatial localization at long times...}, number={17}, journal={MACROMOLECULES}, author={Kenkare, NR and Smith, SW and Hall, CK and Khan, SA}, year={1998}, month={Aug}, pages={5861–5879} } @article{bhatt_hwang_khan_1998, title={Metallocene-based polyolefin foams: effects of oxidative irradiation on mechanical properties}, volume={53}, DOI={10.1016/S0969-806X(98)00208-4}, abstractNote={Metallocene-based polyolefin (MPO) foams are being considered for a wide range of applications because of their uniform composition and low toxicity. In this study, stress relaxation and dynamic rheological experiments are used to probe the effects of oxidative irradiation on the structure and final properties of these novel MPO foams. Experiments conducted on irradiated foams of two different densities reveal significantly different behavior. Gamma irradiation of the lighter foam causes structural degradation due to chain scission reactions. This is manifested in faster stress relaxation rates and lower values of elastic moduli and gel fraction in the irradiated samples. The incorporation of O2 into the polymer backbone, verified by FTIR analysis, confirms the hypothesis of chain scission occurring at the labile peroxide linkages. In contrast, the denser foam shows a small amount of cross-linking and a concomitant improvement in mechanical properties after oxidative irradiation.}, number={5}, journal={RADIATION PHYSICS AND CHEMISTRY}, author={Bhatt, CU and Hwang, CR and Khan, SA}, year={1998}, month={Nov}, pages={539–547} } @misc{gross_givens_jikei_royer_khan_desimone_odell_hamer_1998, title={Synthesis and swelling of poly(bisphenol A carbonate) using supercritical CO2}, volume={31}, number={25}, journal={Macromolecules}, author={Gross, S. M. and Givens, R. D. and Jikei, M. and Royer, J. R. and Khan, S. and Desimone, J. M. and Odell, P. G. and Hamer, G. R.}, year={1998}, month={Dec}, pages={9090–9092} } @article{laurer_mulling_khan_spontak_bukovnik_1998, title={Thermoplastic elastomer gels. I. Effects of composition and processing on morphology and gel behavior}, volume={36}, DOI={10.1002/(sici)1099-0488(19980930)36:13<2379::aid-polb13>3.3.co;2-7}, abstractNote={Thermoplastic elastomer gels (TPEGs) composed of a poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer and a low-volatility, midblock-compatible mineral oil have been investigated at different oil concentrations to ascertain the effect of composition on TPEG morphology and mechanical properties. The impact of thermal processing is also examined by comparing gels thermally quenched to 0°C or slowly cooled to ambient temperature. Transmission electron micrographs reveal that gels with 70 to 90 wt % oil exhibit styrenic micelles measuring ca. 24 nm in diameter. Variation in composition or cooling rate does not have any perceivable effect on micelle size or shape, whereas the rate at which the gels are cooled influences the extent of microstructural order and the time to rupture (tR) at constant strain. Dynamic rheological testing confirms the presence of a physically crosslinked network at TPEG compositions ranging from 70 to 90 wt % oil, independent of cooling rate. Results presented here suggest that the dynamic elastic shear modulus (G′) scales as tαR where α varies from 0.41 to 0.59, depending on cooling rate. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2379–2391, 1998}, number={13}, journal={Journal of Polymer Science. Part B, Polymer Physics}, author={Laurer, J. H. and Mulling, J. F. and Khan, Saad and Spontak, Richard and Bukovnik, R.}, year={1998}, pages={2379–2391} } @article{laurer_mulling_khan_spontak_lin_bukovnik_1998, title={Thermoplastic elastomer gels. II. Effects of composition and temperature on morphology and gel rheology}, volume={36}, DOI={10.1002/(sici)1099-0488(199810)36:14<2513::aid-polb5>3.3.co;2-6}, number={14}, journal={Journal of Polymer Science. Part B, Polymer Physics}, author={Laurer, J. H. and Mulling, J. F. and Khan, Saad and Spontak, Richard and Lin, J. S. and Bukovnik, R.}, year={1998}, pages={2513–2523} } @misc{spontak_roberts_prevysh_khan_1997, title={Method of reducing the viscosity of a black liquor}, volume={5,635,027}, number={1997 June 3}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Spontak, R. J. and Roberts, J. E. and Prevysh, V. A. and Khan, S. A.}, year={1997} } @article{chiou_khan_1997, title={Real-time FTIR and in situ rheological studies on the UV curing kinetics of thiol-ene polymers}, volume={30}, ISSN={["0024-9297"]}, DOI={10.1021/ma9708656}, abstractNote={Real-time FTIR spectroscopy and in situ dynamic rheology were used to characterize the UV curing kinetics of a thiol-ene system containing trimethylolpropane tris(2-mercaptoacetate) and trimethylolpropane diallyl ether. The combination of these two techniques offered a powerful approach for monitoring changes in the chemical and rheological properties of the system during UV curing. Comparable gel times were independently obtained from both FTIR spectroscopy and rheology, thereby validating the comparison of data obtained from each method. The thiol conversion determined from FTIR spectroscopy was correlated with the elastic modulus obtained from rheology. The conversion increased very rapidly during the initial stages of UV curing. However, the elastic modulus did not have an appreciable value until after 65% of the thiol functional groups have reacted, following which the elastic modulus increased at a rapid rate. From the Flory−Stockmayer theory of gelation, the critical thiol conversion at the gel poi...}, number={23}, journal={MACROMOLECULES}, author={Chiou, BS and Khan, SA}, year={1997}, month={Nov}, pages={7322–7328} } @article{prevysh_wang_khan_spontak_1997, title={Salting-in behavior of isotropic and anisotropic aqueous hydroxypropylcellulose solutions}, volume={275}, ISSN={["0303-402X"]}, DOI={10.1007/s003960050082}, number={3}, journal={COLLOID AND POLYMER SCIENCE}, author={Prevysh, VA and Wang, BC and Khan, SA and Spontak, RJ}, year={1997}, month={Mar}, pages={284–287} } @article{raghavan_khan_1997, title={Shear-thickening response of fumed silica suspensions under steady and oscillatory shear}, volume={185}, ISSN={["0021-9797"]}, DOI={10.1006/jcis.1996.4581}, abstractNote={Suspensions of fumed silica in polypropylene glycol exhibit shear-thickening under steady shear and "strain-thickening" under oscillatory shear. Strain-thickening refers to a sharp increase in the complex viscosity eta* observed at critical combinations of strain-amplitude and frequency. Two regimes of strain-thickening behavior have been found: The first occurs at high critical strains and low frequencies, whereas the second occurs at high critical frequencies and a constant lower strain. Strain-thickening in the first regime can be explicitly correlated with steady shear-thickening, using a modified version of the Cox-Merz rule. Accordingly, strain-thickening data for the complex viscosity eta* as a function of the maximum dynamic shear-rate gamma0omega can be superposed against shear-thickening data for the steady viscosity as a function of the steady shear rate. Such a correlation between the two kinds of thickening phenomena has not been reported previously. The combination of shear- and strain-thickening behavior can be qualitatively explained using a clustering mechanism, which attributes the various phenomena to the formation of temporary, flow-induced clusters. The two regimes of strain-thickening are a result of differences in the relative ease of cluster formation.}, number={1}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, author={Raghavan, SR and Khan, SA}, year={1997}, month={Jan}, pages={57–67} } @article{joyce_gilbert_khan_1997, title={The influence of carboxymethylated chitosan on the structure, rheology, and dewatering properties of clay}, volume={80}, number={5}, journal={TAPPI Journal}, author={Joyce, M. K. and Gilbert, R. D. and Khan, S. A.}, year={1997}, pages={185–190} } @article{roberts_spontak_jameel_khan_1996, title={A novel approach to black liquor viscosity reduction using salt additives}, volume={79}, number={8}, journal={TAPPI Journal}, author={Roberts, J.E. and Spontak, R.J. and Jameel, H. and Khan, S.A.}, year={1996}, pages={167–174} } @article{roberts_khan_spontak_1996, title={Controlled black liquor viscosity reduction through salting-in}, volume={42}, ISSN={["0001-1541"]}, DOI={10.1002/aic.690420821}, abstractNote={Abstract}, number={8}, journal={AICHE JOURNAL}, author={Roberts, JE and Khan, SA and Spontak, RJ}, year={1996}, month={Aug}, pages={2319–2326} } @article{nunez_whitfield_mercurio_ilzhoefer_spontak_khan_1996, title={Effect of molecular architecture on DBS-induced block copolymer gels: A rheological study}, volume={106}, ISSN={["1022-1360"]}, DOI={10.1002/masy.19961060126}, abstractNote={Abstract}, journal={MACROMOLECULAR SYMPOSIA}, author={Nunez, CM and Whitfield, JK and Mercurio, DJ and Ilzhoefer, JR and Spontak, RJ and Khan, SA}, year={1996}, month={Apr}, pages={275–286} } @misc{ilzhoefer_broom_nepa_vogler_khan_spontak_1995, title={EVIDENCE OF HIERARCHICAL ORDER IN AN AMPHIPHILIC GRAFT TERPOLYMER GEL}, volume={99}, ISSN={["0022-3654"]}, DOI={10.1021/j100032a002}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEvidence of Hierarchical Order in an Amphiphilic Graft Terpolymer GelJohn R. Ilzhoefer, Brian C. Broom, Stephen M. Nepa, Erwin A. Vogler, Saad A. Khan, and Richard J. SpontakCite this: J. Phys. Chem. 1995, 99, 32, 12069–12071Publication Date (Print):August 1, 1995Publication History Published online1 May 2002Published inissue 1 August 1995https://doi.org/10.1021/j100032a002RIGHTS & PERMISSIONSArticle Views114Altmetric-Citations22LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts}, number={32}, journal={JOURNAL OF PHYSICAL CHEMISTRY}, author={ILZHOEFER, JR and BROOM, BC and NEPA, SM and VOGLER, EA and KHAN, SA and SPONTAK, RJ}, year={1995}, month={Aug}, pages={12069–12071} } @misc{kelly_khan_leduc_tayal_prud'homme_1995, title={Methods and compositions for fracturing subterranean formations}, volume={5,421,412}, number={1995 Jun. 6}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Kelly, R. M. and Khan, S. A. and Leduc, P. and Tayal, A. and Prud'homme, R. K.}, year={1995} } @article{prevysh_spontak_khan_1995, title={Tailored viscosity reduction in aqueous hydroxypropylcellulose solutions}, volume={394}, ISBN={["1-55899-297-9"]}, ISSN={["0272-9172"]}, DOI={10.1557/proc-394-137}, abstractNote={Abstract}, journal={POLYMERS IN MEDICINE AND PHARMACY}, author={Prevysh, VA and Spontak, RJ and Khan, SA}, year={1995}, pages={137–142} } @article{kilpatrick_khan_taya_blackburn, title={A rheological study of polycrystalline lyotropic mesophases in the cesium n-tetradecanoate-water system}, volume={578}, journal={ACS Symposium Series}, author={Kilpatrick, P.K. and Khan, S.A. and Taya, A.l and Blackburn, J.C.}, pages={229–238} } @article{saquing_tang_monian_bonino_manasco_alsberg_khan, title={Alginate-polyethylene oxide blend nanofibers and the role of the carrier polymer in electrospinning}, volume={52}, number={26}, journal={Industrial & Engineering Chemistry Research}, author={Saquing, C. D. and Tang, C. and Monian, B. and Bonino, C. A. and Manasco, J. L. and Alsberg, E. and Khan, S. A.}, pages={8692–8704} } @misc{khan_roberts_royer, title={CO2-assisted deploymerization, purification and recycling of step-growth polymers}, volume={6,919,383}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Khan, S. A. and Roberts, G. W. and Royer, J. R.} } @article{mccutchen_duffaud_leduc_petersen_tayal_khan_kelly, title={Characterization of extremely thermostable enzymatic breakers (alpha-1,6-galactosidase and beta-1,4-mannanase) from the hyperthermophilic bacterium Thermotoga neapolitana 5068 for hydrolysis of guar gum}, volume={52}, number={2}, journal={Biotechnology and Bioengineering}, author={McCutchen, C.M. and Duffaud, G.D. and Leduc, P. and Petersen, A.R.H. and Tayal, A. and Khan, S.A. and Kelly, R.M.}, pages={332–339} } @article{khan_larson, title={Comparison of simple constitutive equations for polymer melts in shear and biaxial and uniaxial extensions}, volume={31}, journal={Journal of Rheology (New York, N.Y.)}, author={Khan, S.A. and Larson, R.G.}, pages={207–234} } @article{khan_prud'homme_larson, title={Comparison of the rheology of polymer melts in shear, and biaxial and uniaxial extensions}, volume={26}, journal={Rheologica Acta}, author={Khan, S.A. and Prud'homme, R.K. and Larson, R.G.}, pages={144–151} } @article{khan_baker_colson, title={Composite polymer electrolytes using fumed silica fillers: Rheology & ionic conductivity}, journal={Chemistry of Materials}, author={Khan, S.A. and Baker, G.L. and Colson, S.}, pages={2359–2363} } @article{wang_ye_yu_kahkoska_zhang_wang_sun_corder_chen_khan_et al., title={Core-Shell Microneedle Gel for Self-Regulated Insulin Delivery}, volume={12}, number={3}, journal={ACS Nano}, author={Wang, J. Q. and Ye, Y. Q. and Yu, J. C. and Kahkoska, A. R. and Zhang, X. D. and Wang, C. and Sun, W. J. and Corder, R. D. and Chen, Z. W. and Khan, S. A. and et al.}, pages={2466–2473} } @article{krishnan_seifert_lee_khan_spontak, title={Cosolvent-regulated time-composition rheological equivalence in blockcopolymer solutions}, volume={6}, number={18}, journal={Soft Matter}, author={Krishnan, A.S. and Seifert, S. and Lee, B. and Khan, S.A. and Spontak, R.J.}, pages={4331–4334} } @article{burns_burroughs_gracz_pritchard_brozena_willoughby_khan, title={Cyclodextrin facilitated electrospun chitosan nanofibers}, volume={5}, number={10}, journal={RSC Advances}, author={Burns, N. A. and Burroughs, M. C. and Gracz, H. and Pritchard, C. Q. and Brozena, A. H. and Willoughby, J. and Khan, S. A.}, pages={7131–7137} } @article{manasco_saquing_tang_khan, title={Cyclodextrin fibers via polymer-free electrospinning}, volume={2}, number={9}, journal={RSC Advances}, author={Manasco, J. L. and Saquing, C. D. and Tang, C. and Khan, S. A.}, pages={3778–3784} } @article{bagley_khan_quinn_barboux_tarascon, title={Dielectric and high Tc superconductor applications of sol-gel and modified sol-gel processing to microelectronics technology}, volume={121}, journal={Journal of Non-crystalline Solids}, author={Bagley, B.G. and Khan, S.A. and Quinn, W.E. and Barboux, P. and Tarascon, J.M.}, pages={454–462} } @article{khan_zoeller, title={Dynamic rheological behavior of flocculated fumed silica suspensions}, volume={37}, number={6}, journal={Journal of Rheology (New York, N.Y.)}, author={Khan, S.A. and Zoeller, N.J.}, pages={1225–1235} } @article{joyce_gilbert_khan, title={Effect of Ca++ ions on the water retention of alginate in paper coatings}, volume={22}, number={4}, journal={Journal of Pulp and Paper Science}, author={Joyce, M. and Gilbert, R. and Khan, S.A.}, pages={J126–J130} } @article{chiou_raghavan_khan, title={Effect of colloidal fillers on the rheology of UV curable polymers: Gel point rheology & the Winter-Chambon criteria}, volume={34}, journal={Macromolecules}, author={Chiou, B.S. and Raghavan, S.R. and Khan, S.A.}, pages={4526–4533} } @article{tang_ozcam_stout_khan, title={Effect of pH on protein distribution in electrospun PVA/BSA composite nanofibers}, volume={13}, number={5}, journal={Biomacromolecules}, author={Tang, C. and Ozcam, A. E. and Stout, B. and Khan, S. A.}, pages={1269–1278} } @article{khan, title={Effect of shear on the gelation of UV curable polymers}, volume={36}, journal={Journal of Rheology (New York, N.Y.)}, author={Khan, S.A.}, pages={573–587} } @article{dufficy_huang_khan_fedkiw, title={Effects of composition and structure on the performance of tin/graphene-containing carbon nanofibers for Li-ion anodes}, volume={7}, number={25}, journal={RSC Advances}, author={Dufficy, M. K. and Huang, S. Y. and Khan, S. A. and Fedkiw, P. S.}, pages={15428–15438} } @article{bonino_krebs_saquing_jeong_shearer_alsberg_khan, title={Electrospinning alginate-based nanofibers: From blends to crosslinked low molecular weight alginate-only systems}, volume={85}, number={1}, journal={Carbohydrate Polymers}, author={Bonino, C.A. and Krebs, M.D. and Saquing, C.D. and Jeong, S.I. and Shearer, K.L. and Alsberg, E. and Khan, S.A.}, pages={111–119} } @article{jeong_krebs_bonino_khan_alsberg, title={Electrospun alginate nanofibers with controlled cell adhesion for tissue engineering}, volume={10}, number={8}, journal={Macromolecular Bioscience}, author={Jeong, S. I. and Krebs, M. D. and Bonino, C. A. and Khan, S. A. and Alsberg, E.}, pages={934–943} } @article{jeong_krebs_bonino_samorezov_khan_alsberg, title={Electrospun chitosan-alginate nanofibers with in situ polyelectrolyte complexation for use as tissue engineering scaffolds}, volume={17}, number={1-2}, journal={Tissue Engineering. Part A}, author={Jeong, S. I. and Krebs, M. D. and Bonino, C. A. and Samorezov, J. E. and Khan, S. A. and Alsberg, E.}, pages={59–70} } @article{saquing_manasco_khan, title={Electrospun nanoparticle-nanofiber composites via a one-step synthesis}, volume={5}, number={8}, journal={Small (Weinheim An Der Bergstrasse, Germany)}, author={Saquing, C. D. and Manasco, J. L. and Khan, S. A.}, pages={944–951} } @article{dufficy_geiger_bonino_khan, title={Electrospun ultrafine fiber composites containing fumed silica: From solution rheology to materials with tunable wetting}, volume={31}, number={45}, journal={Langmuir}, author={Dufficy, M. K. and Geiger, M. T. and Bonino, C. A. and Khan, S. A.}, pages={12455–12463} } @article{higham_tang_landry_pridgeon_lee_andrady_khan, title={Foam electrospinning: A multiple jet, needle-less process for nanofiber production}, volume={60}, number={4}, journal={AIChE Journal}, author={Higham, A. K. and Tang, C. and Landry, A. M. and Pridgeon, M. C. and Lee, E. M. and Andrady, A. L. and Khan, S. A.}, pages={1355–1364} } @article{khan_schnepper_armstrong, title={Foam rheology: III. Measurement of shear flow properties}, volume={32}, journal={Journal of Rheology (New York, N.Y.)}, author={Khan, S.A. and Schnepper, C.A. and Armstrong, R.C.}, pages={69–92} } @article{khan, title={Foam rheology: relation between extensional and shear deformations in high gas fraction foams}, volume={26}, journal={Rheologica Acta}, author={Khan, S.A.}, pages={78–84} } @article{jiang_sun_zhu_burns_khan_mo_gu, title={Furin-mediated sequential delivery of anticancer cytokine and small-molecule drug shuttled by graphene}, volume={27}, number={6}, journal={Advanced Materials}, author={Jiang, T. Y. and Sun, W. J. and Zhu, Q. W. and Burns, N. A. and Khan, S. A. and Mo, R. and Gu, Z.}, pages={1021–1028} } @article{dufficy_khan_fedkiw, title={Galactomannan binding agents for silicon anodes in Li-ion batteries}, volume={3}, number={22}, journal={Journal of Materials Chemistry A}, author={Dufficy, M. K. and Khan, S. A. and Fedkiw, P. S.}, pages={12023–12030} } @article{dufficy_khan_fedkiw, title={Hierarchical graphene-containing carbon nanofibers for lithium-ion battery anodes}, volume={8}, number={2}, journal={ACS Applied Materials & Interfaces}, author={Dufficy, M. K. and Khan, S. A. and Fedkiw, P. S.}, pages={1327–1336} } @article{pirzada_arvidson_saquing_shah_khan, title={Hybrid carbon silica nanofibers through sol-gel electrospinning}, volume={30}, number={51}, journal={Langmuir}, author={Pirzada, T. and Arvidson, S. A. and Saquing, C. D. and Shah, S. S. and Khan, S. A.}, pages={15504–15513} } @article{pirzada_arvidson_saquing_shah_khan, title={Hybrid silica-PVA nanofibers via sol-gel electrospinning}, volume={28}, number={13}, journal={Langmuir}, author={Pirzada, T. and Arvidson, S. A. and Saquing, C. D. and Shah, S. S. and Khan, S. A.}, pages={5834–5844} } @article{talwar_scanu_khan, title={Hydrophobic interactions in associative polymer/nonionic surfactant systems: Effects of surfactant architecture and system parameters}, volume={50}, number={6}, journal={Journal of Rheology (New York, N.Y.)}, author={Talwar, S. and Scanu, L. F. and Khan, S. A.}, pages={831–847} } @article{jeong_burns_bonino_kwon_khan_alsberg, title={Improved cell infiltration of highly porous 3D nanofibrous scaffolds formed by combined fiber-fiber charge repulsions and ultra-sonication}, volume={2}, number={46}, journal={Journal of Materials Chemistry B}, author={Jeong, S. I. and Burns, N. A. and Bonino, C. A. and Kwon, I. K. and Khan, S. A. and Alsberg, E.}, pages={8116–8122} } @article{khan_plitz_frantz, title={In situ technique for monitoring the gelation of UV curable polymers}, volume={31}, journal={Rheologica Acta}, author={Khan, S.A. and Plitz, I.M. and Frantz, R.A.}, pages={151–160} } @article{zhou_fedkiw_khan, title={Interfacial stability between lithium and fumed silica-based composite electrolytes}, volume={149}, journal={Journal of the Electrochemical Society}, author={Zhou, J. and Fedkiw, P. and Khan, S.A.}, pages={A1121–A1126} } @article{mahammad_abdala_roberts_khan, title={Manipulation of hydrophobic interactions in associative polymers using cyclodextrin and enzyme}, volume={6}, number={17}, journal={Soft Matter}, author={Mahammad, S. and Abdala, A. and Roberts, G. W. and Khan, S. A.}, pages={4237–4245} } @article{khan_prud'homme, title={Melt rheology of filled thermoplastics}, volume={4}, journal={Reviews in Chemical Engineering}, author={Khan, S.A. and Prud'homme, R.K.}, pages={205–269} } @article{arvidson_khan_gorga, title={Mesomorphic-R-monoclinic phase transition in isotactic polypropylene: A study of processing effects on structure and mechanical properties}, volume={43}, number={6}, journal={Macromolecules}, author={Arvidson, S.A. and Khan, S.A. and Gorga, R.E.}, pages={2916–2924} } @misc{royer_desimone_roberts_khan, title={Methods of CO2-assisted reactive extrusion}, volume={6,900,267}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Royer, J. and DeSimone, J. M. and Roberts, G. W. and Khan, S. A.} } @article{burns_naclerio_khan_shojaei_raghavan, title={Nanodiamond gels in nonpolar media: Colloidal and rheological properties}, volume={58}, number={5}, journal={Journal of Rheology (New York, N.Y.)}, author={Burns, N. A. and Naclerio, M. A. and Khan, S. A. and Shojaei, A. and Raghavan, S. R.}, pages={1599–1614} } @article{khodabandehlou_tian_luft_khan_desimone, title={Particles for local delivery of proteins using intra-articular route}, volume={5}, number={6}, journal={Advanced Healthcare Materials}, author={Khodabandehlou, K. and Tian, S. M. and Luft, J. C. and Khan, S. A. and DeSimone, J. M.}, pages={653–658} } @article{appaw_gilbert_khan_kadla, title={Phase separation and heat-induced gelation characteristics of cellulose acetate in a mixed solvent system}, volume={17}, number={3}, journal={Cellulose}, author={Appaw, C. and Gilbert, R. D. and Khan, S. A. and Kadla, J. F.}, pages={533–538} } @article{higham_bonino_raghavan_khan, title={Photo-activated ionic gelation of alginate hydrogel: real-time rheological monitoring of the two-step crosslinking mechanism}, volume={10}, number={27}, journal={Soft Matter}, author={Higham, A. K. and Bonino, C. A. and Raghavan, S. R. and Khan, S. A.}, pages={4990–5002} } @article{royer_gay_adam_desimone_khan, title={Polymer melt rheology with high-pressure co2 using a novel magnetically levitated sphere rheometer}, volume={43}, number={8}, journal={Polymer}, author={Royer, J. R. and Gay, Y. J. and Adam, M. and DeSimone, J. M. and Khan, S. A.}, pages={2375–2383} } @article{manasco_tang_burns_saquing_khan, title={Rapidly dissolving poly(vinyl alcohol)/cyclodextrin electrospun nanofibrous membranes}, volume={4}, number={26}, journal={RSC Advances}, author={Manasco, J. L. and Tang, C. and Burns, N. A. and Saquing, C. D. and Khan, S. A.}, pages={13274–13279} } @article{bonino_samorezov_jeon_alsberg_khan, title={Real-time in-situ Rheology of Alginate Hydrogel Photocrosslinking}, volume={7}, number={24}, journal={Soft Matter}, author={Bonino, Christopher and Samorezov, Julia and Jeon, O. and Alsberg, Eben and Khan, Saad}, pages={11510–11517} } @article{larson_khan_raju, title={Relaxation of stress and birefringence in polymers of high molecular weight}, volume={32}, journal={Journal of Rheology (New York, N.Y.)}, author={Larson, R.G. and Khan, S.A. and Raju, V.R.}, pages={145–161} } @article{khan_bagley_barboux_torres, title={Rheological characterization of a sol gel process for the preparation of high Tc superconductors}, volume={155}, journal={Processing Science of Advanced Ceramics}, author={Khan, S.A. and Bagley, B.G. and Barboux, P. and Torres, F.E.}, pages={95–101} } @misc{khan_kiss_mikkelsen, title={Rheological device for in situ measurements of photo polymerization kinetics}, volume={5,105,655}, number={1992 Apr. 21}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Khan, S. A. and Kiss, G. D. and Mikkelsen, K. J.} } @article{khan_rabinovich_prud'homme_sammon_kopylov, title={Rheological monitoring of gelation kinetics of silica sols}, volume={121}, journal={Better Ceramics Through Chemistry III}, author={Khan, S.A. and Rabinovich, E.M. and Prud'homme, R.K. and Sammon, M.J. and Kopylov, N.J.}, pages={73–80} } @article{khan_barboux_bagley_tarascon, title={Rheological study of a gel forming precursor for superconducting YBa2Cu3O7-x}, volume={53}, journal={Applied Physics Letters}, author={Khan, S.A. and Barboux, P. and Bagley, B.G. and Tarascon, J.M.}, pages={700–702} } @article{raghavan_chen_mcdowell_huang_white_khan, title={Rheological study of crosslinking and gelation in chlorobutyl elastomer systems}, volume={37}, number={26}, journal={Polymer}, author={Raghavan, S.R. and Chen, L.A. and McDowell, C. and Huang, R. and White, S. and Khan, S.A.}, pages={5869–5875} } @article{marten_velkovska_khan_ollis, title={Rheological, mass transfer, and mixing characterization of cellulase-producing trichoderma reesei suspensions}, volume={12}, journal={Biotechnology Progress}, author={Marten, M.R. and Velkovska, S. and Khan, S.A. and Ollis, D.F.}, pages={602–611} } @article{frey_cuculo_khan, title={Rheology and gelation of cellulose / ammonia / ammonium thiocyanate solutions}, volume={34}, journal={Journal of Polymer Science. Part B, Polymer Physics}, author={Frey, M.W. and Cuculo, J.A. and Khan, S.A.}, pages={2375–2381} } @article{chiou_english_khan, title={Rheology and photo-cross-linking of thiol-ene polymers}, volume={29}, number={16}, journal={Macromolecules}, author={Chiou, B.-S. and English, R.J. and Khan, S.A.}, pages={5368–5374} } @article{english_jenkins_khan, title={Rheology of a HASE associative polymer and its interaction with non-ionic surfactants}, volume={765}, number={765}, journal={ACS Symposium Series}, author={English, R.J. and Jenkins, R.D. and Khan, S.A.}, pages={369–380} } @article{khan_armstrong, title={Rheology of foams IV. Effect of gas volume fraction}, volume={33}, journal={Journal of Rheology (New York, N.Y.)}, author={Khan, S.A. and Armstrong, R.C.}, pages={881–911} } @article{khan_armstrong, title={Rheology of foams: I. Theory for dry foams}, volume={22}, journal={Journal of Non Newtonian Fluid Mechanics}, author={Khan, S.A. and Armstrong, R.C.}, pages={1–22} } @article{khan_armstrong, title={Rheology of foams: II. Effects of polydispersity and liquid viscosity for foams having gas fraction approaching unity}, volume={25}, journal={Journal of Non Newtonian Fluid Mechanics}, author={Khan, S.A. and Armstrong, R.C.}, pages={61–92} } @article{khan_maruca_plitz, title={Rheology of fumed silica dispersions for fiber optic cables}, volume={31}, journal={Polymer Engineering and Science}, author={Khan, S.A. and Maruca, M.A. and Plitz, I.M.}, pages={1701–1707} } @article{khan_barboux_bagley_torres, title={Rheology of precursors for sol gel derived YBa2Cu3O7-x superconductors}, volume={110}, journal={Journal of Non-crystalline Solids}, author={Khan, S.A. and Barboux, P. and Bagley, B.G. and Torres, F.E.}, pages={142–152} } @article{khan_prud'homme_rabinovich_sammon, title={Rheology of the gelation of fluorine doped silica sols}, volume={110}, journal={Journal of Non-crystalline Solids}, author={Khan, S.A. and Prud'homme, R.K. and Rabinovich, E.M. and Sammon, M.J.}, pages={153–162} } @article{marten_wenger_khan, title={Rheology, mixing time and regime analysis for a production-scale Aspergillus orzyae fermentation}, journal={Bioreactors and Bioprocess Fluid Dynamics}, author={Marten, M.R. and Wenger, K.S. and Khan, S.A.}, pages={295–313} } @article{raghavan_khan, title={Shear-induced microstructure of flocculated suspensions of fumed silica}, volume={39}, number={6}, journal={Journal of Rheology (New York, N.Y.)}, author={Raghavan, S. and Khan, S.A.}, pages={1311–1326} } @article{khodabandehlou_kumbhar_habibi_pandya_luft_khan_desimone, title={Silylated precision particles for controlled release of proteins}, volume={7}, number={10}, journal={ACS Applied Materials & Interfaces}, author={Khodabandehlou, K. and Kumbhar, A. S. and Habibi, S. and Pandya, A. A. and Luft, J. C. and Khan, S. A. and DeSimone, J. M.}, pages={5756–5767} } @article{english_gulati_jenkins_khan, title={Solution rheology of hydrophobically-modified alkali-soluble associative polymers}, volume={41}, number={2}, journal={Journal of Rheology (New York, N.Y.)}, author={English, R.J. and Gulati, H. and Jenkins, R.D. and Khan, S.A.}, pages={427–444} } @article{blanco_lam_smoukov_velikov_khan_velev, title={Stability and viscoelasticity of magneto-pickering foams}, volume={29}, number={32}, journal={Langmuir}, author={Blanco, E. and Lam, S. and Smoukov, S. K. and Velikov, K. P. and Khan, S. A. and Velev, O. D.}, pages={10019–10027} } @article{marten_velkovska_khan_ollis, title={Steady and dynamic shear characterization of cellulase-producing trichoderma reesei suspensions}, volume={51}, number={2}, journal={Applied Biochemistry and Biotechnology}, author={Marten, M.R. and Velkovska, S. and Khan, S.A. and Ollis, D.F.}, pages={319–328} } @article{khan_larson, title={Step planar extension of polymer melts using a lubricated channel}, volume={30}, journal={Rheologica Acta}, author={Khan, S.A. and Larson, R.G.}, pages={16} } @article{bonino_efimenko_jeong_krebs_alsberg_khan, title={Three-dimensional electrospun alginate nanofiber mats via tailored charge repulsions}, volume={8}, number={12}, journal={Small (Weinheim An Der Bergstrasse, Germany)}, author={Bonino, C. A. and Efimenko, K. and Jeong, S. I. and Krebs, M. D. and Alsberg, E. and Khan, S. A.}, pages={1928–1936} } @article{berchtold_reith_khan, title={Torsional stress relaxation in tight-buffered optical fibers}, volume={35}, number={5}, journal={Optical Engineering}, author={Berchtold, K.A. and Reith, L.A. and Khan, S.A.}, pages={1473–1478} } @article{chiou_english_khan, title={UV cross-linking of thiol-ene polymers: A rheological study}, volume={673}, number={673}, journal={ACS Symposium Series}, author={Chiou, B.-S. and English, R.J. and Khan, S.A.}, pages={150–166} } @article{wang_sharma-shivappa_olson_khan, title={Upstream process optimization of polyhydroxybutyrate (PHB) by Alcaligenes latus using two-stage batch and fed-batch fermentation strategies}, volume={35}, number={9}, journal={Bioprocess and Biosystems Engineering}, author={Wang, B. Q. and Sharma-Shivappa, R. R. and Olson, J. W. and Khan, S. A.}, pages={1591–1602} } @article{tayal_kelly_khan, title={Viscosity reduction of hydraulic fracturing fluids through enzymatic hydrolysis}, volume={2}, number={2}, journal={Society of Petroleum Engineers Journal}, author={Tayal, A. and Kelly, R.M. and Khan, S.A.}, pages={204–212} }