@article{kotb_velev_2023, title={Hierarchically reinforced biopolymer composite films as multifunctional plastics substitute}, volume={4}, ISSN={["2666-3864"]}, DOI={10.1016/j.xcrp.2023.101732}, abstractNote={The replacement of synthetic plastics with biodegradable alternatives made from abundant and sustainable raw materials is a challenge of high societal importance. We report a class of high-performance multifunctional composite films made of nano- and microscale reinforced naturally sourced biopolymers. These films are made of an agarose matrix reinforced with hierarchically branched soft dendritic colloids (SDCs) from chitosan. Owing to the highly entangled hierarchical network of the SDC nanofibrils, the reinforced composite has excellent performance with more than 4× higher toughness than non-reinforced agarose, high visible light transmittance, improved hydrostability, and remarkable bactericidal activity. Thus, these reinforced biopolymer composites could match or exceed the excellent mechanical, barrier, and optical properties of common synthetic polymer films. We also demonstrate the soil biodegradability of this composite material in a controlled environment. The results suggest a universal strategy for manufacturing natural-source composite materials that could serve as substitutes for petroleum-based plastics.}, number={12}, journal={CELL REPORTS PHYSICAL SCIENCE}, author={Kotb, Yosra and Velev, Orlin D.}, year={2023}, month={Dec} }
 @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{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{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} }