@misc{agate_williams_dougherty_velev_pal_2023, title={Polymer Color Intelligence: Effect of Materials, Instruments, and Measurement Techniques - A Review}, volume={8}, ISSN={["2470-1343"]}, url={http://dx.doi.org/10.1021/acsomega.2c08252}, DOI={10.1021/acsomega.2c08252}, abstractNote={Transparent polymers and plastics are used to create molded parts and films for many applications. The colors of these products are of great importance for the suppliers, manufacturers, and end-users. However, for simplicity of the processing, the plastics are produced in the form of small pellets or granules. The predictive measurement of the color of such materials is a challenging process and needs consideration of a complex set of factors. A combination of color measurement systems in transmittance and reflectance modes need to be used for such materials, along with the techniques for minimizing the artifacts based on surface texture and particle sizes. This article provides an extensive overview and discussion of the various factors that can affect the perceptive colors and the methods used for the characterization of the colors and minimizing the measuring artifacts.}, number={26}, journal={ACS OMEGA}, publisher={American Chemical Society (ACS)}, author={Agate, Sachin and Williams, Austin and Dougherty, Joseph and Velev, Orlin D. and Pal, Lokendra}, year={2023}, month={Jun}, pages={23257–23270} }
 @article{luiso_petrecca_williams_christopher_velev_pourdeyhimi_fedkiw_2022, title={Structure-Performance Relationships of Li-Ion Battery Fiber-Based Separators}, volume={4}, ISSN={["2637-6105"]}, url={https://doi.org/10.1021/acsapm.2c00216}, DOI={10.1021/acsapm.2c00216}, abstractNote={Lithium-ion battery separators are receiving increased consideration from the scientific community. Many research efforts trend toward creating high-performance fiber-based battery separators with a small and uniform pore size to maximize ionic conductivity and cell discharge capacity. Here, we show that not only the pore size but also the pore size distribution has an important effect on these electrochemical properties. In this work, we studied nonwoven membranes fabricated from a single polymer, poly(vinylidene fluoride) (PVDF), with different pore sizes and pore size distributions using three different techniques (meltblowing, electrospinning, and shear spinning). We evaluate their performance as separators in Li-ion cells. Although meltblowing is commonly employed to produce commercial microfibers/nanofibers, electrospinning has been studied mostly in the academic literature. Shear spinning is an emerging method to fabricate nanofibrous material where, for this study, the morphology of the resulting PVDF membranes may be controlled from fibrous-like to nano-sheet-like with subsequent effects on the electrochemical properties. We show that the smaller the pore size and the wider the pore size distribution, the higher are the electrolyte uptake and ionic conductivity of the mats, resulting in improved in-use discharge capacity and rate capability of Li/LiCoO2 cells.}, number={5}, journal={ACS APPLIED POLYMER MATERIALS}, publisher={American Chemical Society (ACS)}, author={Luiso, Salvatore and Petrecca, Michael J. and Williams, Austin H. and Christopher, Jerush and Velev, Orlin D. and Pourdeyhimi, Behnam and Fedkiw, Peter S.}, year={2022}, month={May}, pages={3676–3686} }
 @article{williams_roh_kotb_velev_2022, title={Superhydrophobic and Anti-Icing Coatings Made of Hierarchically Nanofibrillated Polymer Colloids}, volume={9}, ISSN={["1521-3927"]}, DOI={10.1002/marc.202200513}, abstractNote={AbstractThe deposition of coatings with hierarchical morphology from hydrophobic and hydrophilic polymers is a common approach for making superhydrophobic and superhydrophilic coatings. The water‐repellent, water‐wicking, and anti‐icing coatings reported here are made from a class of materials called soft dendritic colloids (SDCs). The branched, nanofibrous SDCs are produced in suspension through nonsolvent‐induced phase separation in a turbulent medium. The properties of coatings formed by drying ethanol suspensions of SDCs made of polystyrene, polyvinyl alcohol, and polyester are compared. The highly branched SDC morphology creates entangled, porous coating layers with strong physical adhesion to the substrate due to the multitude of nanofiber sub‐contacts analogous to the “gecko leg effect”. Polystyrene SDC coatings show excellent superhydrophobicity but weaker adhesion due to low surface energy. Alternatively, polyvinyl alcohol SDC coatings show superhydrophilicity and strong adhesion from their high surface energy. Two strategies to improve the adhesivity and cohesivity of the SDCs layers are shown effective – use of intertwined networks and of silicone droplet microbinders. The water repulsion, together with the air trapped in the blended superhydrophobic coatings also makes them effective against ice nucleation and adhesion. Finally, these SDCs make thin, flexible, and durable nonwovens with similar properties.}, journal={MACROMOLECULAR RAPID COMMUNICATIONS}, author={Williams, Austin H. and Roh, Sangchul and Kotb, Yosra and Velev, Orlin D.}, year={2022}, month={Sep} }
 @article{williams_hebert_boehm_huddleston_jenkins_velev_nelson_2021, title={Bioscaffold Stiffness Mediates Aerosolized Nanoparticle Uptake in Lung Epithelial Cells}, volume={13}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.1c09701}, abstractNote={In this study, highly porous, ultrasoft polymeric mats mimicking human tissues were formed from novel polyurethane soft dendritic colloids (PU SDCs). PU SDCs have a unique fibrillar morphology controlled by antisolvent precipitation. When filtered from suspension, PU SDCs form mechanically robust nonwoven mats. The stiffness of the SDC mats can be tuned for physiological relevance. The unique physiochemical characteristics of the PU SDC particles dictate the mechanical properties resulting in tunable elastic moduli ranging from 200 to 800 kPa. The human lung A549 cells cultured on both stiff and soft PU SDC membranes were found to be viable, capable of supporting the air-liquid interface (ALI) cell culture, and maintained barrier integrity. Furthermore, A549 cellular viability and uptake efficiency of aerosolized tannic acid-coated gold nanoparticles (Ta-Au) was found to depend on elastic modulus and culture conditions. Ta-Au nanoparticle uptake was twofold and fourfold greater on soft PU SDCs, when cultured at submerged and ALI conditions, respectively. The significant increase in endocytosed Ta-Au resulted in a 20% decrease in viability, and a 4-fold increase in IL-8 cytokine secretion when cultured on soft PU SDCs at ALI. Common tissue culture materials exhibit super-physiological elastic moduli, a factor found to be critical in analyzing nanomaterial cellular interactions and biological responses.}, number={43}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Williams, Austin H. and Hebert, Adrien M. and Boehm, Robert C. and Huddleston, Mary E. and Jenkins, Meghan R. and Velev, Orlin D. and Nelson, M. Tyler}, year={2021}, month={Nov}, pages={50643–50656} }
 @article{luiso_williams_petrecca_roh_velev_fedkiw_2021, title={Poly(Vinylidene Difluoride) Soft Dendritic Colloids as Li-Ion Battery Separators}, volume={168}, ISSN={["1945-7111"]}, url={https://doi.org/10.1149/1945-7111/abdfa7}, DOI={10.1149/1945-7111/abdfa7}, abstractNote={As an alternative to Li-ion battery (LIB) microporous membrane separators that are typically comprised of polyolefins, other materials and separator morphologies may yield increased cell performance. Here, we present a new class of LIB separators comprising poly(vinylidene difluoride) (PVDF)-based and highly branched, colloidal polymer particulates, called soft dendritic colloids, that are produced by shear-driven polymer precipitation within a turbulent nonsolvent flow followed by filtration. We show the morphology of the resulting PVDF particulates may be varied from fibrous dendritic colloids to thin and highly porous sheet-like particles. The use of PVDF leads to low thermal shrinkage (5% at 90 °C) and high tensile strength (<0.7% offset at 1000 psi), while the high porosity (up to 80%) and high particle surface area are responsible for high conductivity (1.2 mS cm−1) and electrolyte uptake (325%), and good cell capacity (112 mAh g−1 in Li/LiCoO2 cell) with <10% loss after 50 cycles. Because shear-driven precipitation with filtration is a facile and versatile process to make a new class of polymeric LIB separators, soft dendritic colloids are promising candidates as separators for next-generation batteries.}, number={2}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, publisher={The Electrochemical Society}, author={Luiso, Salvatore and Williams, Austin H. and Petrecca, Michael J. and Roh, Sangchul and Velev, Orlin D. and Fedkiw, Peter S.}, year={2021}, month={Feb} }
 @article{williams_roh_jacob_stoyanov_hsiao_velev_2021, title={Printable homocomposite hydrogels with synergistically reinforced molecular-colloidal networks}, volume={12}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-021-23098-9}, DOI={10.1038/s41467-021-23098-9}, abstractNote={AbstractThe design of hydrogels where multiple interpenetrating networks enable enhanced mechanical properties can broaden their field of application in biomedical materials, 3D printing, and soft robotics. We report a class of self-reinforced homocomposite hydrogels (HHGs) comprised of interpenetrating networks of multiscale hierarchy. A molecular alginate gel is reinforced by a colloidal network of hierarchically branched alginate soft dendritic colloids (SDCs). The reinforcement of the molecular gel with the nanofibrillar SDC network of the same biopolymer results in a remarkable increase of the HHG’s mechanical properties. The viscoelastic HHGs show >3× larger storage modulus and >4× larger Young’s modulus than either constitutive network at the same concentration. Such synergistically enforced colloidal-molecular HHGs open up numerous opportunities for formulation of biocompatible gels with robust structure-property relationships. Balance of the ratio of their precursors facilitates precise control of the yield stress and rate of self-reinforcement, enabling efficient extrusion 3D printing of HHGs.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Williams, Austin H. and Roh, Sangchul and Jacob, Alan R. and Stoyanov, Simeon D. and Hsiao, Lilian and Velev, Orlin D.}, year={2021}, month={May}, pages={2834} }
 @article{roh_williams_bang_stoyanov_velev_2019, title={Soft dendritic microparticles with unusual adhesion and structuring properties}, volume={18}, ISSN={["1476-4660"]}, DOI={10.1038/s41563-019-0508-z}, abstractNote={The interplay between morphology, excluded volume and adhesivity of particles critically determines the physical properties of numerous soft materials and coatings 1-6 . Branched particles 2  or nanofibres 3 , nanofibrillated cellulose 4  or fumed silica 5  can enhance the structure-building abilities of colloids, whose adhesion may also be increased by capillarity or binding agents 6 . Nonetheless, alternative mechanisms of strong adhesion found in nature involve fibrillar mats with numerous subcontacts (contact splitting) 7-11  as seen in the feet of gecko lizards and spider webs 12-17 . Here, we describe the fabrication of hierarchically structured polymeric microparticles having branched nanofibre coronas with a dendritic morphology. Polymer precipitation in highly turbulent flow results in microparticles with fractal branching and nanofibrillar contact splitting that exhibit gelation at very low volume fractions, strong interparticle adhesion and binding into coatings and non-woven sheets. These soft dendritic particles also have potential advantages for food, personal care or pharmaceutical product formulations.}, number={12}, journal={NATURE MATERIALS}, author={Roh, Sangchul and Williams, Austin H. and Bang, Rachel S. and Stoyanov, Simeon D. and Velev, Orlin D.}, year={2019}, month={Dec}, pages={1315-+} }