@article{davis_genzer_efimenko_abolhasani_2023, title={Continuous Ligand-Free Catalysis Using a Hybrid Polymer Network Support}, volume={7}, ISSN={["2691-3704"]}, url={https://doi.org/10.1021/jacsau.3c00261}, DOI={10.1021/jacsau.3c00261}, abstractNote={Although the pharmaceutical and fine chemical industries primarily utilize batch homogeneous reactions to carry out chemical transformations, emerging platforms seek to improve existing shortcomings by designing effective heterogeneous catalysis systems in continuous flow reactors. In this work, we present a versatile network-supported palladium (Pd) catalyst using a hybrid polymer of poly(methylvinylether-alt-maleic anhydride) and branched polyethyleneimine for intensified continuous flow synthesis of complex organic compounds via heterogeneous Suzuki–Miyaura cross-coupling and nitroarene hydrogenation reactions. The hydrophilicity of the hybrid polymer network facilitates the reagent mass transfer throughout the bulk of the catalyst particles. Through rapid automated exploration of the continuous and discrete parameters, as well as substrate scope screening, we identified optimal hybrid network-supported Pd catalyst composition and process parameters for Suzuki–Miyaura cross-coupling reactions of aryl bromides with steady-state yields up to 92% with a nominal residence time of 20 min. The developed heterogeneous catalytic system exhibits high activity and mechanical stability with no detectable Pd leaching at reaction temperatures up to 95 °C. Additionally, the versatility of the hybrid network-supported Pd catalyst is demonstrated by successfully performing continuous nitroarene hydrogenation with short residence times (<5 min) at room temperature. Room temperature hydrogenation yields of >99% were achieved in under 2 min nominal residence times with no leaching and catalyst deactivation for more than 20 h continuous time on stream. This catalytic system shows its industrial utility with significantly improved reaction yields of challenging substrates and its utility of environmentally-friendly solvent mixtures, high reusability, scalable and cost-effective synthesis, and multi-reaction successes.}, journal={JACS AU}, author={Davis, Bradley A. and Genzer, Jan and Efimenko, Kirill and Abolhasani, Milad}, year={2023}, month={Jul} }
 @article{machikiti_pourdeyhimi_genzer_efimenko_2023, title={Tuning Interfacial Adhesion in Polyester/Polyamide Systems}, volume={7}, ISSN={["1520-5045"]}, url={https://doi.org/10.1021/acs.iecr.3c01517}, DOI={10.1021/acs.iecr.3c01517}, abstractNote={Polymer–polymer adhesion is critical in polymer processing and application areas where lamination, welding, composites, blending, and coextrusion are involved. Polyethylene terephthalate/polyamide (PET/PA) pairs are widely used to produce bicomponent fibers. The strong adhesion due to the formation of chemical bonds in the interfacial region limits post-production fiber processing. The adhesion strength in the PET/PA systems showed that PET/PA66 had the highest adhesion energy, followed by PET/PA6, PET/PA11, and PET/PA12 for all processing conditions. We developed a method that enables adhesion control by introducing a poly(octadecene-alt-maleic anhydride) (POMA) alternating copolymer by either direct interfacial modification or addition into the PET phase. Upon POMA introduction to the system, the reduction in interfacial adhesion strength between PET and polyamides is observed. We established the relationship between adhesion strengths in PET/polyamide systems, processing conditions, and concentration of the POMA modifier.}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Machikiti, Zvikomborero and Pourdeyhimi, Behnam and Genzer, Jan and Efimenko, Kirill}, year={2023}, month={Jul} }
 @article{machikiti_pourdeyhimi_genzer_efimenko_2022, title={Controlling PA6/PET adhesion to facilitate interfacial fracture}, volume={171}, ISSN={["1873-1945"]}, DOI={10.1016/j.eurpolymj.2022.111196}, abstractNote={Microfibers get often produced in the form of bicomponent polymer systems. The materials of choice are Nylon 6 (PA6) and poly(ethylene terephthalate) (PET). This combination of PA6 and PET is preferable because of its beneficial attributes (i.e., thermal stability, mechanical strength, etc.). PA6 and PET exhibit high adhesion when processed at elevated temperatures due to chemical bonds formation by aminolysis of the ester group in PET with a secondary amine in PA6. These fibers are split/fibrillated by mechanical energy (hydroentangling or needle punching). For energy input, it is desirable to have adhesion between the PA6 and PET materials that is not too strong to allow for easy polymer splitting. Therefore, we developed a method for tailoring the PA6/PET interface adhesion by adding modifiers that react preferentially with the PA6 component. The reactivity between PA6 and PET was investigated by spin coating thin films of PA6 and PET on silicon wafers and annealing them at high temperatures. The reaction between PET and small molecules containing secondary amines (i.e., caprolactam, diallyamine, diethylamine, and diisopropylamine) shows a chemical bond between the ester group in PET and the secondary amine group. The poly(styrene-alt-maleic anhydride) (PSMA) and poly(octadecene-alt-maleic anhydride) (POMA) were chosen as model polymer interfacial modifiers. The feasibility of modifying secondary amines is examined by reacting the two modifiers, PSMA and POMA, with small molecules containing secondary amine groups. PA6 and PET display high fracture toughness (i.e., adhesion strength) at elevated temperatures and longer annealing times because of strong interactions between the amine and ester groups in PA6 and PET, respectively. We then assess the adhesion strength between PA6 and PET modified with PSMA and POMA. Both modifiers reduce interfacial adhesion strength between PA6 and PET. Therefore, it is feasible to tailor adhesion at the PA6/PET interface, which could prove helpful in microfibers production.}, journal={EUROPEAN POLYMER JOURNAL}, author={Machikiti, Zvikomborero and Pourdeyhimi, Behnam and Genzer, Jan and Efimenko, Kirill}, year={2022}, month={May} }
 @article{davis_bennett_genzer_efimenko_abolhasani_2022, title={Intensified Hydrogenation in Flow Using a Poly(beta-cyclodextrin) Network-Supported Catalyst}, volume={11}, ISSN={["2168-0485"]}, url={https://doi.org/10.1021/acssuschemeng.2c05467}, DOI={10.1021/acssuschemeng.2c05467}, abstractNote={The intersection of heterogeneous catalysis and flow chemistry is of great importance for the emerging distributed manufacturing of specialty chemicals. Specifically, continuous production of aryl amines is an essential step for on-demand and on-site manufacturing of fine chemicals. This work presents a heterogeneous flow chemistry route for accelerated chemoselective hydrogenation of nitroarenes using a poly(β-cyclodextrin) network-supported palladium catalyst. The developed packed-bed flow reactor enables the selective hydrogenation of a rationally selected library of nitroarenes with >99% yield at room temperature and short residence times (1 min). Utilizing sodium borohydride as the hydrogen carrier in a pressurized packed-bed flow reactor allows safe and efficient delivery of hydrogen to nitroarene molecules. We demonstrate the robustness and versatility of the flow reactor packed with the network-supported catalyst through its consistently high reaction yield over a 3 day run and its reusability and stability in several solvent mixtures with a single-reactor aryl amine manufacturing throughput of up to 31.5 g/day. Furthermore, the catalytic packed-bed reactor is used in a case study for a two-step telescopic synthesis of a critical intermediate for the antibacterial drug linezolid, further supporting its utility as an industrially relevant catalyst for the broad application of catalytic hydrogenations in flow.}, journal={ACS SUSTAINABLE CHEMISTRY & ENGINEERING}, author={Davis, Bradley A. and Bennett, Jeffrey A. and Genzer, Jan and Efimenko, Kirill and Abolhasani, Milad}, year={2022}, month={Nov} }
 @article{rittschof_orihuela_genzer_efimenko_2022, title={PDMS networks meet barnacles: a complex and often toxic relationship}, volume={11}, ISSN={["1029-2454"]}, url={https://doi.org/10.1080/08927014.2022.2145471}, DOI={10.1080/08927014.2022.2145471}, abstractNote={Abstract The biological impact of chemical formulations used in various coating applications is essential in guiding the development of new materials that directly contact living organisms. To illustrate this point, an investigation addressing the impact of chemical compositions of polydimethylsiloxane networks on a common platform for foul-release biofouling management coatings was conducted. The acute toxicity of network components to barnacle larvae, the impacts of aqueous extracts of crosslinker, silicones and organometallic catalyst on trypsin enzymatic activity, and the impact of assembled networks on barnacle adhesion was evaluated. The outcomes of the study indicate that all components used in the formulation of the silicone network alter trypsin enzymatic activity and have a range of acute toxicity to barnacle larvae. Also, the adhesion strength of barnacles attached to PDMS networks correlates to the network formulation protocol. This information can be used to assess action mechanisms and risk–benefit analysis of PDMS networks.}, journal={BIOFOULING}, author={Rittschof, Daniel and Orihuela, Beatriz and Genzer, Jan and Efimenko, Kirill}, year={2022}, month={Nov} }
 @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{bennett_davis_ramezani_genzer_efimenko_abolhasani_2021, title={Continuous Ligand-Free Suzuki-Miyaura Cross-Coupling Reactions in a Cartridge Flow Reactor Using a Gel-Supported Catalyst}, volume={60}, ISSN={["0888-5885"]}, url={https://doi.org/10.1021/acs.iecr.1c01531}, DOI={10.1021/acs.iecr.1c01531}, abstractNote={The Suzuki–Miyaura cross-coupling reaction is one of the most important reactions for pharmaceutical and fine chemical synthesis, performed using both homogeneous and heterogeneous catalysis. In this work, we cross-link poly(methylhydrosiloxane) (PMHS) with tri(ethylene glycol divinyl ether) to create a versatile and readily accessible gel catalyst support for Suzuki–Miyaura cross-coupling reactions in a pseudoheterogeneous manner. The Si–H units present on the PMHS backbone act dually as the cross-linking site and the reducing agent to anchor and reduce palladium(II) acetate to active palladium(0). The PMHS-supported Pd catalyst is then packed into a stainless-steel flow reactor to create a cartridgelike reactor for the continuous operation of a model Suzuki–Miyaura cross-coupling reaction. We systematically investigate the role of reaction temperature, catalyst loading, cross-linking density, and gel particle size on the transient and steady-state behavior of the cartridge flow reactor through an automated flow chemistry platform. The PMHS-supported catalytic particles demonstrate minimal deactivation and leaching over a continuous (80 h) Suzuki–Miyaura cross-coupling reaction at a 30 min nominal residence time at a relatively high reaction temperature of 95 °C. The developed modular flow chemistry strategy equipped with the cartridge flow reactor enables accelerated studies of the fundamental and applied characteristics of gel-supported catalysts while providing increased safety, higher throughput, and removal of the separation step needed for catalyst recovery compared to homogeneous cross-coupling reactions in batch reactors.}, number={26}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, publisher={American Chemical Society (ACS)}, author={Bennett, Jeffrey A. and Davis, Bradley A. and Ramezani, Mahdi and Genzer, Jan and Efimenko, Kirill and Abolhasani, Milad}, year={2021}, month={Jul}, pages={9418–9428} }
 @article{clark_thacker_mcgill_miles_westmoreland_efimenko_genzer_santiso_2021, title={DFT Analysis of Organotin Catalytic Mechanisms in Dehydration Esterification Reactions for Terephthalic Acid and 2,2,4,4-Tetramethyl-1,3-cyclobutanediol}, volume={125}, ISSN={["1520-5215"]}, url={https://doi.org/10.1021/acs.jpca.1c00850}, DOI={10.1021/acs.jpca.1c00850}, abstractNote={Polyesters synthesized from 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) and terephthalic acid (TPA) are improved alternatives to toxic polycarbonates based on bisphenol A. In this work, we use ωB97X-D/LANL2DZdp calculations, in the presence of a benzaldehyde polarizable continuum model solvent, to show that esterification of TMCD and TPA will reduce and subsequently dehydrate a dimethyl tin oxide catalyst, becoming ligands on the now four-coordinate complex. This reaction then proceeds most plausibly by an intramolecular acyl-transfer mechanism from the tin complex, aided by a coordinated proton donor such as hydronium. These findings are a key first step in understanding polyester synthesis and avoiding undesirable side reactions during production.}, number={23}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, publisher={American Chemical Society (ACS)}, author={Clark, Jennifer A. and Thacker, Pranav J. and McGill, Charles J. and Miles, Jason R. and Westmoreland, Phillip R. and Efimenko, Kirill and Genzer, Jan and Santiso, Erik E.}, year={2021}, month={Jun}, pages={4943–4956} }
 @article{castillo_dickey_gorman_genzer_efimenko_2021, title={Deposition of silicate coatings on poly(ethylene terephthalate) for improved scratch and solvent resistance}, volume={10}, ISSN={["1097-4628"]}, url={https://doi.org/10.1002/app.51800}, DOI={10.1002/app.51800}, abstractNote={Abstract}, journal={JOURNAL OF APPLIED POLYMER SCIENCE}, publisher={Wiley}, author={Castillo, Gilbert A. and Dickey, Michael D. and Gorman, Christopher B. and Genzer, Jan and Efimenko, Kirill}, year={2021}, month={Oct} }
 @article{zboray_efimenko_jones_genzer_2021, title={Functional Gels Containing Hydroxamic Acid Degrade Organophosphates in Aqueous Solutions}, volume={60}, ISSN={["0888-5885"]}, DOI={10.1021/acs.iecr.1c01374}, abstractNote={We synthesized poly(maleic anhydride-co-methyl vinyl ether) (PMAMVE) gels and functionalized them to form hydroxamic acid functional groups. We evaluated the performance of the gels in decomposing dimethyl nitrophenyl phosphate (DMNP). We monitored organophosphate degradation kinetics as a function of gel chemical composition, cross-linking density, and solution pH and applied Thiele modulus analysis to determine the importance of transport phenomena related to the particulate gel size. The decomposition of DMNP in the maleic anhydride gels followed pseudo-first-order kinetics for all studied conditions. The performance was influenced by the spatial confinement of the hydroxamic acid groups inside the gel. The gels made of PMAMVE copolymers modified with hydroxamic acid offer a robust new system with high degradation efficiency, scalability, and preparation simplicity.}, number={24}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Zboray, Steven and Efimenko, Kirill and Jones, Jacob L. and Genzer, Jan}, year={2021}, month={Jun}, pages={8799–8811} }
 @article{walker_pandiyarajan_efimenko_genzer_2019, title={Generating Surface-Anchored Zwitterionic Networks and Studying Their Resistance to Bovine Serum Albumin Adsorption}, volume={1}, ISSN={["2637-6105"]}, DOI={10.1021/acsapm.9b00772}, abstractNote={We report a simple method to generate surface-anchored zwitterionic network coatings that exhibit low nonspecific protein adsorption. We first synthesize amphiphilic random copolymers comprising 2-(dimethylamino)ethyl methacrylate (DMAEMA) and propargyl methacrylate (PGMA) units in two different nominal molar ratios (50:50 and 75:25) by free radical copolymerization. The DMAEMA moieties in the copolymers are then betainized with 1,3-propane sultone to obtain zwitterionic macromolecules. We create substrate-anchored network coatings by casting thin copolymer films (∼100 nm) containing 2 wt % of photoactive benzophenone onto a polystyrene substrate and cross-link them by UV-light irradiation at 365 nm (UV dose = 9–10 J/cm2). We investigate the cross-linking reaction with infrared spectroscopy, monitor the change in film thickness, and study the swelling behavior of the coatings as a function of ionic strength and electrolyte using spectroscopic ellipsometry. We demonstrate the performance of such surface-at...}, number={12}, journal={ACS APPLIED POLYMER MATERIALS}, author={Walker, Edwin J., Jr. and Pandiyarajan, C. K. and Efimenko, Kirill and Genzer, Jan}, year={2019}, month={Dec}, pages={3323–3333} }
 @article{datta_efimenko_genzer_2019, title={Thermally driven directional free-radical polymerization in confined channels}, volume={10}, ISSN={["1759-9962"]}, url={https://doi.org/10.1039/C8PY01550C}, DOI={10.1039/c8py01550c}, abstractNote={We report on the formation of poly(acrylamide) (PAAm) with a relatively-narrow molecular weight distribution (MWD) by means of thermally-driven directional free-radical polymerization carried out in polymerization chambers featuring two parallel glass walls separated by various distances, ranging from sub-millimeter to a few millimeters.}, number={8}, journal={POLYMER CHEMISTRY}, publisher={Royal Society of Chemistry (RSC)}, author={Datta, Preeta and Efimenko, Kirill and Genzer, Jan}, year={2019}, month={Feb}, pages={920–925} }
 @article{castillo_wilson_efimenko_dickey_gorman_genzer_2016, title={Amidation of Polyesters Is Slow in Nonaqueous Solvents: Efficient Amidation of Poly(ethylene terephthalate) with 3-Aminopropyltriethoxysilane in Water for Generating Multifunctional Surfaces}, volume={8}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/ACSAMI.6B12155}, DOI={10.1021/ACSAMI.6B12155}, abstractNote={This paper describes surface functionalization of poly(ethylene terephthalate) (PET) films by transamidation of the ester groups with primary amines. The use of water as a solvent improves tremendously the reaction rate and yield compared to conventionally used alcohols. In this study, PET films were exposed to an aqueous solution of 3-aminopropyltriethoxysilane (APTES), which resulted in ester-to-amide reactions on the surface of the film. Hydrolysis of the resulting ethoxy moieties in APTES creates hydroxyl groups that can be used as anchoring points for further modification of PET films. This scheme offers an alternative approach to modify polyesters using water as the solvent.}, number={51}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Castillo, Gilbert A. and Wilson, Lance and Efimenko, Kirill and Dickey, Michael D. and Gorman, Christopher B. and Genzer, Jan}, year={2016}, month={Dec}, pages={35641–35649} }
 @article{oezcam_efimenko_spontak_fischer_genzer_2016, title={Multipurpose Polymeric Coating for Functionalizing Inert Polymer Surfaces}, volume={8}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.5b12216}, abstractNote={In this work, we report on the development of a highly functionalizable polymer coating prepared by the chemical coupling of trichlorosilane (TCS) to the vinyl groups of poly(vinylmethyl siloxane) (PVMS). The resultant PVMS-TCS copolymer can be coated as a functional organic primer layer on a variety of polymeric substrates, ranging from hydrophilic to hydrophobic. Several case studies demonstrating the remarkable and versatile properties of PVMS-TCS coatings are presented. In particular, PVMS-TCS is found to serve as a convenient precursor for the deposition of organosilanes and the subsequent growth of polymer brushes, even on hydrophobic surfaces, such as poly(ethylene terephthalate) and polypropylene. In this study, the physical and chemical characteristics of these versatile PVMS-TCS coatings are interrogated by an arsenal of experimental probes, including scanning electron microscopy, water contact-angle measurements, ellipsometry, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy.}, number={8}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Oezcam, A. Evren and Efimenko, Kirill and Spontak, Richard J. and Fischer, Daniel A. and Genzer, Jan}, year={2016}, month={Mar}, pages={5694–5705} }
 @article{cruz-teran_carlin_efimenko_genzer_rao_2016, title={Targeted Mutagenesis and Combinatorial Library Screening Enables Control of Protein Orientation on Surfaces and Increased Activity of Adsorbed Proteins}, volume={32}, ISSN={["0743-7463"]}, DOI={10.1021/acs.langmuir.6b01446}, abstractNote={While nonspecific adsorption is widely used for immobilizing proteins on solid surfaces, the random nature of protein adsorption may reduce the activity of immobilized proteins due to occlusion of the active site. We hypothesized that the orientation a protein assumes on a given surface can be controlled by systematically introducing mutations into a region distant from its active site, thereby retaining activity of the immobilized protein. To test this hypothesis, we generated a combinatorial protein library by randomizing six targeted residues in a binding protein derived from highly stable, nonimmunoglobulin Sso7d scaffold; mutations were targeted in a region that is distant from the binding site. This library was screened to isolate binders that retain binding to its cognate target (chicken immunoglobulin Y, cIgY) as well as exhibit adsorption on unmodified silica at pH 7.4 and high ionic strength conditions. A single mutant, Sso7d-2B5, was selected for further characterization. Sso7d-2B5 retained binding to cIgY with an apparent dissociation constant similar to that of the parent protein; both mutant and parent proteins saturated the surface of silica with similar densities. Strikingly, however, silica beads coated with Sso7d-2B5 could achieve up to 7-fold higher capture of cIgY than beads coated with the parent protein. These results strongly suggest that mutations introduced in Sso7d-2B5 alter its orientation relative to the parent protein, when adsorbed on silica surfaces. Our approach also provides a generalizable strategy for introducing mutations in proteins so as to improve their activity upon immobilization, and has direct relevance to development of protein-based biosensors and biocatalysts.}, number={34}, journal={LANGMUIR}, author={Cruz-Teran, Carlos A. and Carlin, Kevin B. and Efimenko, Kirill and Genzer, Jan and Rao, Balaji M.}, year={2016}, month={Aug}, pages={8660–8667} }
 @article{özçam_efimenko_genzer_2014, title={Effect of ultraviolet/ozone treatment on the surface and bulk properties of poly(dimethyl siloxane) and poly(vinylmethyl siloxane) networks}, volume={55}, ISSN={0032-3861}, url={http://dx.doi.org/10.1016/J.POLYMER.2014.05.027}, DOI={10.1016/J.POLYMER.2014.05.027}, abstractNote={We present a comparative study aiming at comprehending the effect of ultraviolet/ozone treatment on the modification of poly(dimethyl siloxane) (PDMS) and poly(vinylmethyl siloxane) (PVMS) silicone elastomers networks (SENs). Both PDMS and PVMS SENs undergo dramatic changes in their properties when exposed to UVO. The surface chemical composition of both PDMS and PVMS at long UVO treatment times changes substantially and features a high density of hydrophilic groups. There are two major differences in behavior in the two classes of materials. First, relative to PDMS, the PVMS-based SENs get modified throughout the entire bulk. Second, the physico-chemical changes detected in PVMS take place on much shorter time scale relative to PDMS. These results are in accord with our earlier reports that indicated that when exposed to UVO, the topmost ≈5 nm of PDMS gets converted into a silica-like material, which then acts as a barrier for diffusion of atomic oxygen. In this case, the bulk of PDMS maintains its elasticity. In contrast, both the surface and bulk of PVMS films undergo substantial changes in properties when exposed to UVO. First, the surface modification of PVMS SENs takes place after only a few seconds of the UVO treatment. In addition, we register substantial modification of bulk properties, including the complete densification accompanied with increased bulk modulus. Likely, the susceptibility of the vinyl bonds to radical reactions is responsible for this effect.}, number={14}, journal={Polymer}, publisher={Elsevier BV}, author={Özçam, A. Evren and Efimenko, Kirill and Genzer, Jan}, year={2014}, month={Jun}, pages={3107–3119} }
 @article{johnson_gao_shields_smith_efimenko_cushing_genzer_lopez_2013, title={Elastomeric microparticles for acoustic mediated bioseparations}, volume={11}, ISSN={["1477-3155"]}, DOI={10.1186/1477-3155-11-22}, abstractNote={Abstract}, journal={JOURNAL OF NANOBIOTECHNOLOGY}, author={Johnson, Leah M. and Gao, Lu and Shields, C. Wyatt and Smith, Margret and Efimenko, Kirill and Cushing, Kevin and Genzer, Jan and Lopez, Gabriel P.}, year={2013}, month={Jun} }
 @article{efimenko_oezcam_genzer_fischer_phelan_douglas_2013, title={Self-assembly fronts in collision: impinging ordering organosilane layers}, volume={9}, ISSN={["1744-6848"]}, DOI={10.1039/c2sm27600c}, abstractNote={Colliding autocatalytic wave-fronts of self-assembling organosilane (OS) layers are generated through the controlled positioning of sources of the volatile OS material at the edges of a silica wafer and through adjustment of the container dimensions in which the wafer sources are placed. The concentration profiles and molecular orientation of the OS colliding wave-fronts are assessed by means of combinatorial near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. For systems involving self-assembly wave-fronts developing from the same OS precursor molecule, the shapes of interfacial region arising from front collision are centro-symmetrical and slowly ‘heal’ to form a uniform OS layer. In contrast, heterogeneous systems, involving OS molecules having different chemistries exhibit different rates of advance and highly non-symmetrical concentration profiles after front collision. We discuss the general nature of our OS colliding front data in terms of a mean field model of colliding reaction–diffusion fronts that generalizes a model introduced before for describing single OS front propagation.}, number={8}, journal={SOFT MATTER}, author={Efimenko, Kirill and Oezcam, Ali E. and Genzer, Jan and Fischer, Daniel A. and Phelan, Fredrick R., Jr. and Douglas, Jack F.}, year={2013}, pages={2493–2505} }
 @article{peng_efimenko_genzer_parsons_2012, title={Oligomer Orientation in Vapor-Molecular-Layer-Deposited Alkyl-Aromatic Polyamide Films}, volume={28}, ISSN={["0743-7463"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000306441100019&KeyUID=WOS:000306441100019}, DOI={10.1021/la3017936}, abstractNote={The surface-limited molecular-layer deposition of alkyl-aromatic polyamide films using sequential doses of 1,4-butane diamine (BDA) and terephthaloyl dichloride (TDC) is characterized using in situ quartz crystal microbalance and ex situ spectroscopy analysis. For the first time, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to offer insight into molecular orientation in films deposited via molecular-layer deposition (MLD). The results show that the oligomer units are lying nearly parallel to the surface, which differs from the linear vertical growth mode often used to illustrate film growth.}, number={28}, journal={LANGMUIR}, author={Peng, Qing and Efimenko, Kirill and Genzer, Jan and Parsons, Gregory N.}, year={2012}, month={Jul}, pages={10464–10470} }
 @article{datta_efimenko_genzer_2012, title={The effect of confinement on thermal frontal polymerization}, volume={3}, ISSN={["1759-9954"]}, DOI={10.1039/c2py20640d}, abstractNote={In thermal frontal polymerization, the interplay between heat diffusion and Arrhenius type reaction kinetics gives rise to a propagating reactive front that is effectively sustained through a system positive feedback mechanism. We seek to understand how spatial confinement affects the system dynamics and overall polymerization kinetics. We find that with increasing confinement of the system, the front propagation velocity decreases and the nearly “parabolic” front profile flattens out. While in bulk or unconfined systems the convective heat and mass transfer effects are responsible for higher heat generation rates and higher temperature gradients, leading to faster front propagation, the convection is significantly suppressed in highly confined systems. Consequently, a smaller number of radicals are generated, resulting in a slower propagation step and long polymer chains.}, number={12}, journal={POLYMER CHEMISTRY}, author={Datta, Preeta and Efimenko, Kirill and Genzer, Jan}, year={2012}, month={Dec}, pages={3243–3246} }
 @article{bonino_efimenko_jeong_krebs_alsberg_khan_2012, title={Three-Dimensional Electrospun Alginate Nanofiber Mats via Tailored Charge Repulsions}, volume={8}, ISSN={1613-6810}, url={http://dx.doi.org/10.1002/smll.201101791}, DOI={10.1002/smll.201101791}, abstractNote={Abstract}, number={12}, journal={Small}, publisher={Wiley}, author={Bonino, Christopher A. and Efimenko, Kirill and Jeong, Sung In and Krebs, Melissa D. and Alsberg, Eben and Khan, Saad A.}, year={2012}, month={Mar}, pages={1928–1936} }
 @article{genzer_arifuzzaman_bhat_efimenko_ren_szleifer_2012, title={Time Dependence of Lysozyme Adsorption on End-Grafted Polymer Layers of Variable Grafting Density and Length}, volume={28}, ISSN={["0743-7463"]}, DOI={10.1021/la2038747}, abstractNote={A combined experimental and theoretical approach establishes the long-lived nature of protein adsorption on surfaces coated with chemically grafted macromolecules. Specifically, we monitor the time dependence of adsorption of lysozyme on surfaces comprising polymer assemblies made of poly(2-hydroxyethyl methacrylate) brushes grafted onto flat silica surfaces such that they produce patterns featuring orthogonal and gradual variation of the chain length (N) and grafting density (σ). We show that in the kinetically controlled regime, the amount of adsorbed protein scales universally with the product σN, while at equilibrium the amount of adsorbed protein is governed solely by σ. Surprisingly, for moderate concentrations of protein in solution, adsorption takes more than 72 h to reach an equilibrium, or steady state. Our experimental findings are corroborated with predictions using molecular theory that provides further insight into the protein adsorption phenomenon. The theory predicts that the universal behavior observed experimentally should be applicable to polymers in poor and theta solvents and to a limited extent also to good solvent conditions. Our combined experimental and theoretical findings reveal that protein adsorption is a long-lived phenomenon, much longer than generally assumed. Our studies confirm the previously predicted important differences in behavior for the kinetic versus thermodynamic control of protein adsorption.}, number={4}, journal={LANGMUIR}, author={Genzer, Jan and Arifuzzaman, Shafi and Bhat, Rajendra R. and Efimenko, Kirill and Ren, Chun-lai and Szleifer, Igal}, year={2012}, month={Jan}, pages={2122–2130} }
 @article{yang_ozcam_efimenko_genzer_2011, title={Photochromic materials with tunable color and mechanical flexibility}, volume={7}, ISSN={["1744-683X"]}, DOI={10.1039/c0sm00928h}, abstractNote={Florescence switches based on photochromic compounds have been fabricated previously and identified as potential candidates for information technology. Recently, optically responsive materials with tunable color have been prepared by dissolving photochromic compounds, such as spiropyran (SP), into solutions of various pH or embedding them into sol–gel matrices with adjusted chemical compositions. Here we report on fabricating flexible rubbers with tunable color by embedding SP molecules inside silicone elastomer networks (SENs) based on poly(vinylmethylsiloxane) (PVMS). SP-containing PVMS networks have been further modified either physically by exposing them to ultraviolet/ozone treatment or chemically by attaching functional thiols to the vinyl bonds in PVMS via UV-activated thiol–ene addition. The color hue of the SP–PVMS SENs after exposing to UV light depends on either the UVO dose or the chemical end-functionality of the thiol modifier, respectively. We also present simple methodologies enabling patterning regions in SP-doped SENs with various shapes and colors.}, number={8}, journal={SOFT MATTER}, author={Yang, Hyun-Kwan and Ozcam, A. Evren and Efimenko, Kirill and Genzer, Jan}, year={2011}, pages={3766–3774} }
 @article{ahmed_yang_ozcam_efimenko_weiger_genzer_haugh_2011, title={Poly(vinylmethylsiloxane) Elastomer Networks as Functional Materials for Cell Adhesion and Migration Studies}, volume={12}, ISSN={["1526-4602"]}, DOI={10.1021/bm101549y}, abstractNote={Cell migration is central to physiological responses to injury and infection and in the design of biomaterial implants. The ability to tune the properties of adhesive materials and relate those properties in a quantitative way to the dynamics of intracellular processes remains a definite challenge in the manipulation of cell migration. Here, we propose the use of poly(vinylmethylsiloxane) (PVMS) networks as novel substrata for cell adhesion and migration. These materials offer the ability to tune independently chemical functionality and elastic modulus. Importantly, PVMS networks are compatible with total internal reflection fluorescence (TIRF) microscopy, which is ideal for interrogating the cell-substratum interface; this latter characteristic presents a distinct advantage over polyacrylamide gels and other materials that swell with water. To demonstrate these capabilities, adhesive peptides containing the arginyl-glycyl-aspartic acid (RGD) tripeptide motif were successfully grafted to the surface of PVMS network using a carboxyl-terminated thiol as a linker. Peptide-specific adhesion, spreading, and random migration of NIH 3T3 mouse fibroblasts were characterized. These experiments show that a peptide containing the synergy sequence of fibronectin (PHSRN) in addition to RGD promotes more productive cell migration without markedly enhancing cell adhesion strength. Using TIRF microscopy, the dynamics of signal transduction through the phosphoinositide 3-kinase pathway were monitored in cells as they migrated on peptide-grafted PVMS surfaces. This approach offers a promising avenue for studies of directed migration and mechanotransduction at the level of intracellular processes.}, number={4}, journal={BIOMACROMOLECULES}, publisher={American Chemical Society (ACS)}, author={Ahmed, Shoeb and Yang, Hyun-kwan and Ozcam, Ali E. and Efimenko, Kirill and Weiger, Michael C. and Genzer, Jan and Haugh, Jason M.}, year={2011}, month={Apr}, pages={1265–1271} }
 @article{hoeger_rojas_efimenko_velev_kelley_2011, title={Ultrathin film coatings of aligned cellulose nanocrystals from a convective-shear assembly system and their surface mechanical properties}, volume={7}, ISSN={1744-683X 1744-6848}, url={http://dx.doi.org/10.1039/c0sm01113d}, DOI={10.1039/c0sm01113d}, abstractNote={Ultrathin films of aligned cellulose nanocrystals (CNCs) were deposited on solid supports by using convective and shear forces. Compared to previous systems involving high electric or magnetic fields to control the orientation of these rod-like natural nanoparticles, the proposed process of alignment was very simple, inexpensive and with potential for scale up. The effect of concentration of CNC in aqueous suspensions, type of solid support, relative humidity and rates of withdrawal of the deposition plate were determined by using atomic force microscopy (AFM) and ellipsometry. The degree of orientation was quantified from the number density of CNCs in leading angles by using image analyses. Also, the contribution of shear and capillary forces on alignment parallel and normal to the withdrawal direction was elucidated. The best alignment of CNCs in the withdrawal direction, favored by shear effects, was achieved with gold and silica supports with a pre-adsorbed cationic polyelectrolyte layer and at a CNC suspension concentration above 2.5% (w/w), below the critical concentration for chiral nematic phase separation. Compared to the bare solid support, nanoindentation of the obtained coatings of ultrathin films of oriented CNCs provided enhanced surface mechanical strength and wear resistance. A transverse Young's modulus, hardness and coefficient of friction of 8.3 ± 0.9 GPa, 0.38 ± 0.03 GPa and 0.51 ± 0.23 GPa, respectively, were measured. Notably, the transverse Young's modulus was found to be in agreement with reported values predicted by molecular modeling and measured for single CNCs by using atomic force microscopy.}, number={5}, journal={Soft Matter}, publisher={Royal Society of Chemistry (RSC)}, author={Hoeger, Ingrid and Rojas, Orlando J. and Efimenko, Kirill and Velev, Orlin D. and Kelley, Steve S.}, year={2011}, pages={1957} }
 @article{zoppe_habibi_rojas_venditti_johansson_efimenko_österberg_laine_2010, title={Poly(<i>N</i>-isopropylacrylamide) Brushes Grafted from Cellulose Nanocrystals via Surface-Initiated Single-Electron Transfer Living Radical Polymerization}, volume={11}, ISSN={1525-7797 1526-4602}, url={http://dx.doi.org/10.1021/bm100719d}, DOI={10.1021/bm100719d}, abstractNote={Cellulose nanocrystals (CNCs) or nanowhiskers produced from sulfuric acid hydrolysis of ramie fibers were used as substrates for surface chemical functionalization with thermoresponsive macromolecules. The CNCs were grafted with poly(N-isopropylacrylamide) brushes via surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) under various conditions at room temperature. The grafting process was confirmed via Fourier transform IR spectroscopy and X-ray photoelectron spectroscopy and the different molecular masses of the grafts were quantified and found to depend on the initiator and monomer concentrations used. No observable damage occurred to the CNCs after grafting, as determined by X-ray diffraction. Size exclusion chromatography analyses of polymer chains cleaved from the cellulose nanocrystals indicated that a higher degree of polymerization was achieved by increasing initiator or monomer loading, most likely caused by local heterogeneities yielding higher rates of polymerization. It is expected that suspension stability, interfacial interactions, friction, and other properties of grafted CNCs can be controlled by changes in temperature and provide a unique platform for further development of stimuli-responsive nanomaterials.}, number={10}, journal={Biomacromolecules}, publisher={American Chemical Society (ACS)}, author={Zoppe, Justin O. and Habibi, Youssef and Rojas, Orlando J. and Venditti, Richard A. and Johansson, Leena-Sisko and Efimenko, Kirill and Österberg, Monika and Laine, Janne}, year={2010}, month={Sep}, pages={2683–2691} }
 @article{efimenko_finlay_callow_callow_genzer_2009, title={Development and Testing of Hierarchically Wrinkled Coatings for Marine Antifouling}, volume={1}, ISSN={["1944-8252"]}, DOI={10.1021/am9000562}, abstractNote={We report on the formation and testing of novel marine coatings comprising hierarchically wrinkled surface topographies (HWTS) having wrinkles of different length scales (generations) ranging from tens of nanometers to a fraction of a millimeter. The individual wrinkle generations are arranged in nested patterns, where each larger wrinkle resides underneath and represents a scaled-up version of the smaller wrinkle. We present and discuss results from field tests in seawater and laboratory experiments. The results of our field tests reveal that while coatings with flat topographies foul after relatively short time periods (4-15 weeks), the HWST coatings with the same chemistries as flat coatings remain relatively free of biofouling even after prolonged exposure to seawater (18 months). In contrast to flat coatings, the HWST substrates are not colonized by barnacles. These observations suggest that surface topography plays a dominant role in governing the coating defense against barnacle fouling even without fine-tuning the chemical composition of the overcoat. Laboratory experiments indicate that settlement of zoospores of the green alga Ulva and the strength of attachment of sporelings (young plants) depend on the chemical composition of the coating as well as surface topography.}, number={5}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Efimenko, Kirill and Finlay, John and Callow, Maureen E. and Callow, James A. and Genzer, Jan}, year={2009}, month={May}, pages={1031–1040} }
 @article{arifuzzaman_oezcam_efimenko_fischer_genzer_2009, title={Formation of surface-grafted polymeric amphiphilic coatings comprising ethylene glycol and fluorinated groups and their response to protein adsorption}, volume={4}, ISSN={["1559-4106"]}, DOI={10.1116/1.3114502}, abstractNote={Amphiphilic polymer coatings were prepared by first generating surface-anchored polymer layers of poly(2-hydroxyethyl methacrylate) (PHEMA) on top of flat solid substrates followed by postpolymerization reaction on the hydroxyl terminus of HEMA’s pendent group using three classes of fluorinating agents, including organosilanes, acylchlorides, and trifluoroacetic anhydride (TFAA). The distribution of the fluorinated groups inside the polymer brushes was assessed by means of a suite of analytical probes, including contact angle, ellipsometry, infrared spectroscopy, atomic force microscopy, and near-edge x-ray absorption fine structure spectroscopy. While organosilane modifiers were found to reside primarily close to the tip of the brush, acylchlorides penetrated deep inside PHEMA thus forming random copolymers P(HEMA-co-fHEMA). The reaction of TFAA with the PHEMA brush led to the formation of amphiphilic diblocks, PHEMA-b-P(HEMA-co-fHEMA), whose bottom block comprised unmodified PHEMA and the top block was made of P(HEMA-co-fHEMA) rich in the fluorinated segments. This distribution of the fluorinated groups endowed PHEMA-b-P(HEMA-co-fHEMA) with responsive properties; while in hydrophobic environment P(HEMA-co-fHEMA) segregated to the surface, when in contact with a hydrophilic medium, PHEMA partitioned at the brush surface. The surface activity of the amphiphilic coatings was tested by studying the adsorption of fibrinogen (FIB). While some FIB adsorption occurred on most coatings, the ones made by TFAA modification of PHEMA remained relatively free of FIB.}, number={2}, journal={BIOINTERPHASES}, author={Arifuzzaman, Shafi and Oezcam, Ali E. and Efimenko, Kirill and Fischer, Daniel A. and Genzer, Jan}, year={2009}, month={Jun}, pages={FA33–FA44} }
 @article{ozcam_efimenko_jaye_spontak_fischer_genzer_2009, title={Modification of PET surfaces with self-assembled monolayers of organosilane precursors}, volume={172}, ISSN={["1873-2526"]}, DOI={10.1016/j.elspec.2009.03.012}, abstractNote={Abstract We report on a facile, robust and rapid method by which poly(ethylene terephthalate) (PET) surfaces can be chemically modified while avoiding chemical degradation. Specifically, we demonstrate that brief exposure of PET surfaces to ultraviolet/ozone (UVO) generates a large surface concentration of hydrophilic moieties that serve as points of chemical attachment, thereby facilitating subsequent chemisorption of organosilane precursors. The feasibility of this methodology is tested by decorating UVO-modified PET surfaces with semifluorinated organosilane (SFOS) molecules, which serve to alter the surface energy of PET without compromising its bulk characteristics. The physico-chemical properties of the SFOS layers attached to PET are studied with a palette of experimental probes, including near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle, atomic force microscopy (AFM), and ellipsometry. Experimental results indicate that ≈2 min of UVO treatment is optimal for covering PET with dense self-assembled monolayers (SAMs) of SFOS. Longer UVO treatment times contaminate and correspondingly roughen PET surfaces with low-molecular-weight organic compounds (LMWOCs) generated from degradation of the topmost PET material. As a consequence, SFOS SAMs attached to the LMWOC layer readily wash off from UVO-treated PET.}, number={1-3}, journal={JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA}, author={Ozcam, Ali E. and Efimenko, Kirill and Jaye, Cherno and Spontak, Richard J. and Fischer, Daniel A. and Genzer, Jan}, year={2009}, month={May}, pages={95–103} }
 @article{park_efimenko_sjoblom_genzer_2009, title={Rapid Removal of Organics and Oil Spills from Waters Using Silicone Rubber "Sponges"}, volume={30}, ISSN={["1532-2351"]}, DOI={10.1080/01932690802540384}, abstractNote={We have developed a simple, robust, and efficient technology utilizing cheap and recoverable materials based on commercially available silicone elastomer networks for removing organic solvents and crude oil from waters. Hydrophobic and oleophilic properties of silicone elastomers endow poly(dimethyl siloxane) (PDMS) with the capacity to absorb a large variety of organics, including benzene (B), toluene (T), ethylbenzene (E), and xylene (X), commonly referred to as BTEX, and also crude oils, while at the same time enabling the organic “sponges” to float on waters, which facilitates straightforward handling. We developed a method for generating PDMS particles with variable sizes (ranging from hundreds nanometers to few millimeters) by drop-wise depositing siloxane/cross-linker mixtures into warm water, a process which leads to the cross-linking of the PDMS components. We have tested the capability of the PDMS particles to remove toluene and benzene from water. We also performed similar experiments by utilizing PDMS sheets. In both instances we observed a rapid sorption of the organic phase into PDMS; the amount of absorbed organic solvent depended on the concentration in water and the total mass (volume) of PDMS and did not depend on the geometry of the PDMS “sponge.” In addition, we have examined the uptake of toluene and benzene from toluene/benzene (T/B) mixtures dissolved in water. Our results indicate that the amount of benzene absorbed from the T/B mixtures into PDMS increases relative to the uptake from pure benzene/water solutions. This behavior is associated with toluene acting as a “surfactant” that effectively replaces the more unfavorable PDMS/B contacts with less costly T/B ones. Finally, a simple experiment demonstrates qualitatively that PDMS is also capable of removing crude oils from oil-contaminated waters.}, number={3}, journal={JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY}, author={Park, Insun and Efimenko, Kirill and Sjoblom, Johan and Genzer, Jan}, year={2009}, pages={318–327} }
 @article{guo_resnick_efimenko_genzer_desimone_2008, title={Alternative fluoropolymers to avoid the challenges associated with perfluorooctanoic acid}, volume={47}, ISSN={["0888-5885"]}, DOI={10.1021/ie0703179}, abstractNote={The degradation of stain-resistant coating materials leads to the release of biopersistent perfluorooctanoic acid (PFOA) to the environment. In order to find the environmentally friendly substitutes, we have designed and synthesized a series of nonbiopersistant fluorinated polymers containing perfluorobutyl groups in the side chains. The surface properties of the new coating materials were characterized by static and dynamic contact angle measurements. The new coating materials demonstrate promising hydrophobic and oleophobic properties with low surfaces tensions. The wetting properties and surface structure of the polymers were tuned by varying the “spacer” structures between the polymer backbones and the perfluorinated groups of the side chains. The relationship between orientations of the fluorinated side chains and performances of polymer surfaces were further investigated by near-edge X-ray fine absorption structure (NEXAFS) experiments and differential scanning calorimetry (DSC).}, number={3}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Guo, Ji and Resnick, Paul and Efimenko, Kirill and Genzer, Jan and DeSimone, Joseph M.}, year={2008}, month={Feb}, pages={502–508} }
 @inproceedings{crowe_efimenko_genzer_2007, title={Manipulating siloxane surfaces: Obtaining the desired surface function via engineering design}, volume={964}, DOI={10.1021/bk-2007-0964.ch015}, abstractNote={We present a synopsis of recent accomplishment in our group in the area of surface-functionalized silicone elastomer networks. Specifically, we show that by combining mechanical manipulation of poly(dimethylsiloxane) (PDMS) networks with activation via ultraviolet/ozone (UVO) treatment and subsequent chemical modification of the preactivated surfaces, one can generate so-called mechanically assembled monolayers (MAMs). This technology can be successfully applied to create a variety of surfaces, including dense polymer brushes, long-lived superhydrophobic surfaces, molecular gradients comprising tunable length scales and two-dimensional chemical gradients. In addition, the UVO modification of mechanically strained PDMS sheets provides a convenient route for creating "buckled" elastomeric sheets. These surfaces have a multitude of applications; ranging from anti-fouling surfaces to directed particle assembly. Finally we demonstrate control of surface wettability and responsiveness using poly(vinylmethylsiloxane) (PVMS) networks. We have shown that PVMS surfaces can be chemically tailored by reacting with thiols. The degree of response (including response rate) of such surfaces to hydrophobic-hydrophilic interactions can be adjusted by varying the chemical and structural properties of the side-group modifiers.}, booktitle={Science and technology of silicones and silicone-modified materials}, author={Crowe, J. A. and Efimenko, Kirill and Genzer, Jan}, year={2007}, pages={222–255} }
 @misc{liebmann-vinson_chaney_efimenko_genzer_2007, title={Methods of surface modification of a flexible substrate to enhance cell adhesion}, volume={7,198,855}, number={2007 Apr. 7}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Liebmann-Vinson, A. and Chaney, B. and Efimenko, K. and Genzer, J.}, year={2007} }
 @article{douglas_efimenko_fischer_phelan_genzer_2007, title={Propagating waves of self-assembly in organosilane monolayers}, volume={104}, ISSN={["0027-8424"]}, DOI={10.1073/pnas.0703620104}, abstractNote={
            Wavefronts associated with reaction–diffusion and self-assembly processes are ubiquitous in the natural world. For example, propagating fronts arise in crystallization and diverse other thermodynamic ordering processes, in polymerization fronts involved in cell movement and division, as well as in the competitive social interactions and population dynamics of animals at much larger scales. Although it is often claimed that self-sustaining or autocatalytic front propagation is well described by mean-field “reaction–diffusion” or “phase field” ordering models, it has recently become appreciated from simulations and theoretical arguments that fluctuation effects in lower spatial dimensions can lead to appreciable deviations from the classical mean-field theory (MFT) of this type of front propagation. The present work explores these fluctuation effects in a real physical system. In particular, we consider a high-resolution near-edge x-ray absorption fine structure spectroscopy (NEXAFS) study of the spontaneous frontal self-assembly of organosilane (OS) molecules into self-assembled monolayer (SAM) surface-energy gradients on oxidized silicon wafers. We find that these layers organize from the wafer edge as propagating wavefronts having well defined velocities. In accordance with two-dimensional simulations of this type of front propagation that take fluctuation effects into account, we find that the interfacial widths
            w
            (
            t
            ) of these SAM self-assembly fronts exhibit a power-law broadening in time,
            w
            (
            t
            ) ≈
            t
            β
            , rather than the constant width predicted by MFT. Moreover, the observed exponent values accord rather well with previous simulation and theoretical estimates. These observations have significant implications for diverse types of ordering fronts that occur under confinement conditions in biological or materials-processing contexts.
          }, number={25}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Douglas, Jack F. and Efimenko, Kirill and Fischer, Daniel A. and Phelan, Fredrick R. and Genzer, Jan}, year={2007}, month={Jun}, pages={10324–10329} }
 @article{smith_efimenko_fischer_lappi_kilpatrick_genzer_2007, title={Study of the packing density and molecular orientation of bimolecular self-assembled monolayers of aromatic and aliphatic organosilanes on silica}, volume={23}, ISSN={["0743-7463"]}, DOI={10.1021/la062475v}, abstractNote={Bimolecular self-assembled monolayers (SAMs) of aromatic and aliphatic chlorosilanes were self-assembled onto silica, and their characteristics were established by contact angle measurement, near-edge X-ray absorption fine structure spectroscopy, and Fourier transform infrared spectroscopy. Three aromatic constituents (phenyltrichlorosilane, benzyltrichlorosilane, and phenethyltrichlorosilane) were studied in combination with four aliphatic coadsorbates (butyltrichlorosilane, butyldimethylchlorosilane, octadecyltrichlorosilane, and octadecyldimethylchlorosilane). Our results demonstrate that whereas SAMs made of trichlorinated organosilanes are densely packed, SAMs prepared from monochlorinated species are less dense and poorly ordered. In mixed systems, trichlorinated aromatics and trichlorinated aliphatics formed SAMs with highly tunable compositions; their surfaces were compositionally homogeneous with no large-scale domain separation. The homogeneous nature of the resulting SAM was a consequence of the formation of in-plane siloxane linkages among neighboring molecules. In contrast, when mixing monochlorinated aliphatics with trichlorinated aromatics, molecular segregation occurred. Although the two shortest aromatic species did not display significant changes in orientation upon mixing with aliphatics, the aromatic species with the longest polymethylene spacer, phenethyltrichlorosilane, displayed markedly different orientation behavior in mixtures of short- and long-chain aliphatics.}, number={2}, journal={LANGMUIR}, author={Smith, Matthew B. and Efimenko, Kirill and Fischer, Daniel A. and Lappi, Simon E. and Kilpatrick, Peter K. and Genzer, Jan}, year={2007}, month={Jan}, pages={673–683} }
 @article{kim_efimenko_genzer_carbonell_2007, title={Surface properties of poly[2-(perfluorooctyl)ethyl acrylate] deposited from liquid CO2 high-pressure free meniscus coating}, volume={40}, ISSN={["1520-5835"]}, DOI={10.1021/ma0623791}, abstractNote={The surface characteristics of poly[2-(perfluorooctyl)ethyl acrylate] (PFOEA) films deposited using a high-pressure free meniscus coating (hFMC) process with liquid CO{sub 2} (l-CO{sub 2}) as the coating solvent on 12.5 cm diameter silicon wafer substrates were investigated using contact angle measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy. The results were compared with surface property measurements of PFOEA films deposited from 1,1,2-trichlorotrifluoroethane (Freon 113) under normal dip coating conditions at atmospheric pressure. NEXAFS measurements showed that perfluoroalkyl groups in the films from l-CO{sub 2} and Freon 113 were well-organized and oriented normal to the substrate at the air/polymer interface. AFM images and XPS measurements revealed that a terrace-like structure of the PFOEA film from l-CO{sub 2} resulted in carbonyl group exposure at the air/polymer interface. This leads to smaller contact angles on the films cast from l-CO{sub 2} relative to the specimens deposited from Freon 113. Annealing the films deposited from the solvents resulted in droplet formation on the surface due to dewetting. The critical surface tension ({gamma}{sub c}) after annealing the film prepared from Freon 113 increased from 6.5 to 8.5 mJ/m{sup 2}, whereas {gamma}{sub c} of the film deposited frommore » l-CO{sub 2} decreased slightly from 9.7 to 8.9 mJ/m{sup 2}. We discuss how surface morphology changes before and after annealing play a role in the variation of {gamma}{sub c}.« less}, number={3}, journal={MACROMOLECULES}, author={Kim, Jaehoon and Efimenko, Kirill and Genzer, Jan and Carbonell, Ruben G.}, year={2007}, month={Feb}, pages={588–597} }
 @article{genzer_efimenko_fischer_2006, title={Formation mechanisms and properties of semifluorinated molecular gradients on silica surfaces}, volume={22}, ISSN={["0743-7463"]}, DOI={10.1021/la061016r}, abstractNote={The goal of this study is to elucidate the formation of molecular gradients made of semifluorinated organosilanes (SFOs) on flat substrates by using a methodology developed by Chaudhury and Whitesides (Science 1992, 256, 1539). We use surface-sensitive combinatorial near-edge X-ray absorption fine structure (combi-NEXAFS) spectroscopy to measure the position-dependent concentration and orientation of SFO molecules in SFO molecular gradients on flat silica surfaces. Using the combi-NEXAFS data, we establish the correlation between the fraction of the F(CF(2))(8)(CH(2))(2)- species on the substrate and the average tilt angle of the -(CF(2))(8)F group in the SFO as a function of the deposition gas medium (air vs nitrogen) and the end group around the silicon atom (monofunctional vs trifunctional). In addition, we utilize the gradient geometry to comprehend the mechanism of formation of SFO self-assembled monolayers (SAMs). Specifically, we provide evidence that depending on the nature of the end group in the SFO and the vapor phase the SFO molecules add themselves into the existing SAMs either as individual molecules or as multimolecular complexes.}, number={20}, journal={LANGMUIR}, author={Genzer, Jan and Efimenko, Kirill and Fischer, Daniel A.}, year={2006}, month={Sep}, pages={8532–8541} }
 @article{clare_efimenko_fischer_genzer_abbott_2006, title={Orientations of liquid crystals in contact with surfaces that present continuous gradients of chemical functionality}, volume={18}, ISSN={["1520-5002"]}, DOI={10.1021/cm052537n}, abstractNote={We report the formation of continuous spatial gradients in the density of grafted semifluorinated chains on silicon oxide surfaces by vapor-phase diffusion of semifluorinated silanes. We quantify the orientations of the nematic liquid crystal (LC) 4-cyano-4‘-pentylbiphenyl on these surfaces as a function of local surface composition obtained by using NEXAFS. These measurements demonstrate that it is possible to obtain the full range of tilt angles of a LC on these surfaces. We also use the data provided by these gradient surfaces to test hypotheses regarding the nature of the interaction between the LC and surfaces that give rise to the range of tilted orientations of the LC. We conclude that the orientations of the LC are not determined solely by the density of grafted semifluorinated chains or by the density of residual hydroxyl groups presented at these surfaces following reactions with the silanes. Instead, our results raise the possibility that the tilt angles of the semifluorinated chains on these s...}, number={9}, journal={CHEMISTRY OF MATERIALS}, author={Clare, BH and Efimenko, K and Fischer, DA and Genzer, J and Abbott, NL}, year={2006}, month={May}, pages={2357–2363} }
 @misc{genzer_efimenko_2006, title={Recent developments in superhydrophobic surfaces and their relevance to marine fouling: a review}, volume={22}, ISSN={["1029-2454"]}, DOI={10.1080/08927010600980223}, abstractNote={Abstract In this review, a brief synopsis of superhydrophobicity (i.e. extreme non-wettability) and its implications on marine fouling are presented. A short overview of wettability and recent experimental developments aimed at fabricating superhydrophobic surfaces by tailoring their chemical nature and physical appearance (i.e. substratum texture) are reviewed. The formation of responsive/“smart” surfaces, which adjust their physico-chemical properties to variations in some outside physical stimulus, including light, temperature, electric field, or solvent, is also described. Finally, implications of tailoring the surface chemistry, texture, and responsiveness of surfaces on the design of effective marine fouling coatings are considered and discussed.}, number={5}, journal={BIOFOULING}, author={Genzer, Jan and Efimenko, Kirill}, year={2006}, pages={339–360} }
 @article{tomlinson_efimenko_genzer_2006, title={Study of kinetics and macroinitiator efficiency in surface-initiated atom-transfer radical polymerization}, volume={39}, ISSN={["0024-9297"]}, DOI={10.1021/ma061885n}, abstractNote={Generation of surface-tethered block copolymer brushes with well-defined physicochemical characteristics requires achieving good control over the degree of polymerization of each block of the copolymer. In order to precisely form these block copolymer layers, one must (1) utilize a polymerization scheme that is capable of generating nearly monodisperse polymers, (2) fully characterize the kinetics of surface-initiated polymerization, and (3) produce macroinitiators with living characteristics capable of reinitiating the growth of each subsequent block. In this work, we describe technological steps leading to the controlled growth of surface-tethered homopolymers and multiblock copolymers via surface-initiated atom transfer radical polymerization (ATRP) from flat substrates. We first report on investigating the ability of a macroinitiator to reinitiate a homopolymer brush. We use computer simulations to illustrate the advantages of an “added deactivator” type ATRP over the traditional “sacrificial initiato...}, number={26}, journal={MACROMOLECULES}, author={Tomlinson, Michael R. and Efimenko, Kirill and Genzer, Jan}, year={2006}, month={Dec}, pages={9049–9056} }
 @article{efimenko_rackaitis_manias_vaziri_mahadevan_genzer_2005, title={Nested self-similar wrinkling patterns in skins}, volume={4}, ISSN={["1476-4660"]}, DOI={10.1038/nmat1342}, abstractNote={Stiff thin films on soft substrates are both ancient and commonplace in nature; for instance, animal skin comprises a stiff epidermis attached to a soft dermis. Although more recent and rare, artificial skins are increasingly used in a broad range of applications, including flexible electronics, tunable diffraction gratings, force spectroscopy in cells, modern metrology methods, and other devices. Here we show that model elastomeric artificial skins wrinkle in a hierarchical pattern consisting of self-similar buckles extending over five orders of magnitude in length scale, ranging from a few nanometres to a few millimetres. We provide a mechanism for the formation of this hierarchical wrinkling pattern, and quantify our experimental findings with both computations and a simple scaling theory. This allows us to harness the substrates for applications. In particular, we show how to use the multigeneration-wrinkled substrate for separating particles based on their size, while simultaneously forming linear chains of monodisperse particles.}, number={4}, journal={NATURE MATERIALS}, author={Efimenko, K and Rackaitis, M and Manias, E and Vaziri, A and Mahadevan, L and Genzer, J}, year={2005}, month={Apr}, pages={293–297} }
 @article{carla_wang_hussain_efimenko_genzer_grant_sarti_carbonell_doghieri_2005, title={Nonequilibrium model for sorption and swelling of bulk glassy polymer films with Supercritical carbon dioxide}, volume={38}, ISSN={["1520-5835"]}, DOI={10.1021/ma0506684}, abstractNote={A new procedure is introduced for the calculation of solubility isotherms of plasticizing agents in glassy polymer matrices with particular application to the case of absorption of supercritical gases in bulk glassy polymer films. The model presented is an extension of the nonequilibrium thermodynamics for glassy polymers (NET-GP) approach, modified to allow for the calculation of the effects of pressure, temperature, and gas concentration on the glass transition. Mass sorption and one- dimensional swelling behavior are analyzed for the carbon dioxide (CO2)-poly(methyl methacrylate) (PMMA) system at high pressure. A quantitative comparison is presented between the model performance and experimental data measured using quartz crystal microbalance (QCM) and high-pressure ellipsometry (HPE).}, number={24}, journal={MACROMOLECULES}, author={Carla, V and Wang, K and Hussain, Y and Efimenko, K and Genzer, J and Grant, C and Sarti, GC and Carbonell, RG and Doghieri, F}, year={2005}, month={Nov}, pages={10299–10313} }
 @article{efimenko_crowe_manias_schwark_fischer_genzer_2005, title={Rapid formation of soft hydrophilic silicone elastomer surfaces}, volume={46}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2005.07.046}, abstractNote={We report on the rapid formation of hydrophilic silicone elastomer surfaces by ultraviolet/ozone (UVO) irradiation of poly(vinylmethyl siloxane) (PVMS) network films. Our results reveal that the PVMS network surfaces render hydrophilic upon only a short UVO exposure time (seconds to a few minutes). We also provide evidence that the brief UVO irradiation treatment does not cause dramatic changes in the surface modulus of the PVMS network. We compare the rate of formation of hydrophilic silicone elastomer surfaces made of PVMS to those of model poly(dimethyl siloxane) (PDMS) and commercial-grade PDMS (Sylgard-184). We find that relative to PVMS, 20 times longer UVO treatment times are needed to oxidize the PDMS network surfaces in order to achieve a comparable density of surface-bound hydrophilic moieties. The longer UVO treatment times for PDMS are in turn responsible for the dramatic increase in surface modulus of UVO treated PDMS, relative to PVMS. We also study the formation of self-assembled monolayers (SAMs) made of semifluorinated organosilane precursors on the PVMS-UVO and PDMS-UVO network surfaces. By tuning the UVO treatment times and by utilizing mono- and tri-functional organosilanes we find that while mono-functionalized organosilanes attach directly to the substrate, SAMs of tri-functionalized organosilanes form in-plane networks on the underlying UVO-modified silicone elastomer surface, even with only short UVO exposure times.}, number={22}, journal={POLYMER}, author={Efimenko, K and Crowe, JA and Manias, E and Schwark, DW and Fischer, DA and Genzer, J}, year={2005}, month={Oct}, pages={9329–9341} }
 @article{fischer_efimenko_bhat_sambasivan_genzer_2004, title={Mapping surface chemistry and molecular orientation with combinatorial near-edge X-ray absorption fine structure spectroscopy}, volume={25}, ISSN={["1521-3927"]}, DOI={10.1002/marc.200300178}, abstractNote={Abstract}, number={1}, journal={MACROMOLECULAR RAPID COMMUNICATIONS}, author={Fischer, DA and Efimenko, K and Bhat, RR and Sambasivan, S and Genzer, J}, year={2004}, month={Jan}, pages={141–149} }
 @misc{genzer_efimenko_2004, title={Methods for forming tunable molecular gradients on substrates}, volume={6,770,323}, number={2004 Aug. 03}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Genzer, J. and Efimenko, K.}, year={2004} }
 @article{fleming_ulrich_efimenko_genzer_chan_madey_oh_zhou_rowe_2004, title={Near-edge absorption fine structure and UV photoemission spectroscopy studies of aligned single-walled carbon nanotubes on Si(100) substrates}, volume={22}, ISSN={["2166-2746"]}, DOI={10.1116/1.1775190}, abstractNote={We report near-edge absorption fine structure (NEXAFS) and UV photoemission spectroscopy (UPS) studies of aligned single-walled carbon nanotube films on Si(100) substrates. Orientation of the films was detected in the NEXAFS spectra, with the intensity of the π* core exciton at 284.4 eV showing a strong dependence on nanotube alignment with respect to the polarization of the incident radiation. At lower angles of incidence, the intensity of the π* peak was higher for all orientations, which we attribute to the greater accessibility of the π* orbitals. UPS spectra of the films showed little angular dependence and included features consistent with the total density of states of graphite. As a result of the nanotube curvature and the distribution of nanotube chiralities, the UPS spectra are similar to angle-integrated graphite spectra.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Fleming, L and Ulrich, MD and Efimenko, K and Genzer, J and Chan, ASY and Madey, TE and Oh, SJ and Zhou, O and Rowe, JE}, year={2004}, pages={2000–2004} }
 @article{wu_tomlinson_efimenko_genzer_2003, title={A combinatorial approach to surface anchored polymers}, volume={38}, ISSN={["1573-4803"]}, DOI={10.1023/A:1027373216389}, number={22}, journal={JOURNAL OF MATERIALS SCIENCE}, author={Wu, T and Tomlinson, M and Efimenko, K and Genzer, J}, year={2003}, month={Nov}, pages={4471–4477} }
 @article{genzer_fischer_efimenko_2003, title={Combinatorial near-edge x-ray absorption fine structure: Simultaneous determination of molecular orientation and bond concentration on chemically heterogeneous surfaces}, volume={82}, ISSN={["1077-3118"]}, DOI={10.1063/1.1535271}, abstractNote={We show that simultaneous molecular orientation and bond chemistry of planar chemically heterogeneous surfaces can be obtained by combining near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and rastering the incident x-ray beam on the specimen. This rastering produces serially two-dimensional NEXAFS images in space and energy, revealing information about the chemistry (including bond concentration) and orientation of the surface-bound molecules with submillimeter planar spatial resolution and submonolayer molecular sensitivity. We illustrate the power of the combinatorial NEXAFS method by simultaneously probing the concentration and molecular orientation of semifluorinated (SF) molecules in double-SF molecular gradients on flat silica substrates.}, number={2}, journal={APPLIED PHYSICS LETTERS}, author={Genzer, J and Fischer, DA and Efimenko, K}, year={2003}, month={Jan}, pages={266–268} }
 @article{wu_efimenko_vlcek_subr_genzer_2003, title={Formation and properties of anchored polymers with a gradual variation of grafting densities on flat substrates}, volume={36}, ISSN={["1520-5835"]}, DOI={10.1021/ma0257189}, abstractNote={We show that assemblies comprising anchored polymers with a gradual variation of grafting densities on solid substrates can be generated by first covering the substrate with a molecular gradient of the polymerization initiator, followed by polymerization from the substrate-bound initiator centers (“grafting from”). We apply this technique to prepare grafting density gradients of poly(acrylamide) (PAAm) on flat silica substrates. We demonstrate that using the grafting density gradient geometry, the mushroom-to-brush transition can be accessed on a single sample. This transition is detected by monitoring the dependence of the thickness of the grafted PAAm in a good solvent using variable angle spectroscopic ellipsometry. Wettability experiments performed on the gradient PAAm substrate provide complementary information about the nature of the mushroom-to-brush transition.}, number={7}, journal={MACROMOLECULES}, author={Wu, T and Efimenko, K and Vlcek, P and Subr, V and Genzer, J}, year={2003}, month={Apr}, pages={2448–2453} }
 @article{wu_efimenko_genzer_2002, title={Combinatorial study of the mushroom-to-brush crossover in surface anchored polyacrylamide}, volume={124}, ISSN={["0002-7863"]}, DOI={10.1021/ja027412n}, abstractNote={We present a method for fabricating anchored polymers with a gradual variation of grafting densities on solid substrates. The technique for generating such structures comprises (i) formation of a molecular gradient of polymerization initiator on the solid substrate and (ii) polymerization from the substrate-bound initiator centers ("grafting from"). We measure the mushroom-to-brush transition in grafted polyacrylamides and show that the mushroom and brush behavior can be described using existing scaling theories.}, number={32}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Wu, T and Efimenko, K and Genzer, J}, year={2002}, month={Aug}, pages={9394–9395} }
 @article{genzer_efimenko_fischer_2002, title={Molecular orientation and grafting density in semifluorinated self-assembled monolayers of mono-, di-, and trichloro silanes on silica substrates}, volume={18}, ISSN={["0743-7463"]}, DOI={10.1021/la025921x}, abstractNote={Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to measure the molecular orientation in semifluorinated self-assembled monolayers (SAMs) prepared by vapor deposition of mono- (F3C(CF2)8(CH2)2Si(CH3)2Cl, m-F8H2), di- (F3C(CF2)8(CH2)2Si(CH3)Cl2, d-F8H2), and trichloroorganosilanes (F3C(CF2)8(CH2)2SiCl3, t-F8H2) on flat silica-covered substrates. The average tilt angles (from the sample normal) of the fluorocarbon part, F(CF2)8-, of t-F8H2, d-F8H2, and m-F8H2 measured by carbon K-edge NEXAFS are 10 ± 2°, 35 ± 2°, and 45 ± 3°, respectively. We show that the increase of the tilt angle is associated with the steric hindrance of the methyl groups attached to silicon close to the bonding substrate. We also show that the molecular orientation obtained from the NEXAFS measurements can be used to estimate the grafting densities of the F8H2 molecules on the substrates. We present a simple one-dimensional geometric model to show that the grafting density of m-F8H2 is approximately one-half of t...}, number={24}, journal={LANGMUIR}, author={Genzer, J and Efimenko, K and Fischer, DA}, year={2002}, month={Nov}, pages={9307–9311} }
 @article{efimenko_wallace_genzer_2002, title={Surface modification of Sylgard-184 poly(dimethyl siloxane) networks by ultraviolet and ultraviolet/ozone treatment}, volume={254}, DOI={10.1006/jcis.202.8594}, number={2}, journal={Journal of Colloid and Interface Science}, author={Efimenko, Kirill and Wallace, W. E. and Genzer, Jan}, year={2002}, pages={306–315} }
 @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} }