@article{roh_yeo_bang_han_velikov_velev_2024, title={Transparency-changing elastomers by controlling of the refractive index of liquid inclusions}, volume={36}, ISSN={["1361-648X"]}, DOI={10.1088/1361-648X/ad6110}, abstractNote={Complex materials that change their optical properties in response to changes in environmental conditions can find applications in displays, smart windows, and optical sensors. Here a class of biphasic composites with stimuli-adaptive optical transmittance is introduced. The biphasic composites comprise aqueous droplets (a mixture of water, glycerol, and surfactant) embedded in an elastomeric matrix. The biphasic composites are tuned to be optically transparent through a careful match of the refractive indices between the aqueous droplets and the elastomeric matrix. We demonstrate that stimuli (e.g., salinity and temperature change) can trigger variations in the optical transmittance of the biphasic composite. The introduction of such transparency-changing soft matter with liquid inclusions offers a novel approach to designing advanced optical devices, optical sensors, and metamaterials.}, number={42}, journal={JOURNAL OF PHYSICS-CONDENSED MATTER}, author={Roh, Sangchul and Yeo, Seonju and Bang, Rachel S. and Han, Koohee and Velikov, Krassimir P. and Velev, Orlin D.}, year={2024}, month={Oct} }
 @article{basu_okello_castellanos_roh_velev_2023, title={Assembly and manipulation of responsive and flexible colloidal structures by magnetic and capillary interactions}, volume={3}, ISSN={["1744-6848"]}, DOI={10.1039/d3sm00090g}, abstractNote={The long-ranged interactions induced by magnetic fields and capillary forces in multiphasic fluid–particle systems facilitate the assembly of a rich variety of colloidal structures and materials.}, journal={SOFT MATTER}, author={Basu, Abhirup and Okello, Lilian B. B. and Castellanos, Natasha and Roh, Sangchul and Velev, Orlin D. D.}, year={2023}, month={Mar} }
 @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{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_okello_golbasi_hankwitz_liu_tracy_velev_2019, title={3D-Printed Silicone Soft Architectures with Programmed Magneto-Capillary Reconfiguration}, volume={4}, ISSN={["2365-709X"]}, DOI={10.1002/admt.201800528}, abstractNote={AbstractSoft intelligent structures that are programmed to reshape and reconfigure under magnetic field can find applications such as in soft robotics and biomedical devices. Here, a new class of smart elastomeric architectures that undergo complex reconfiguration and shape change in applied magnetic fields, while floating on the surface of water, is reported. These magnetoactive soft actuators are fabricated by 3D printing with homocomposite silicone capillary ink. The ultrasoft actuators easily deform by the magnetic force exerted on carbonyl iron particles embedded in the silicone, as well as lateral capillary forces. The tensile and compressive moduli of the actuators are easily determined by their topological design through 3D printing. As a result, their responses can be engineered by the interplay of the intensity of the magnetic field gradient and the programmable moduli. 3D printing allows us to fabricate soft architectures with different actuation modes, such as isotropic/anisotropic contraction and multiple shape changes, as well as functional reconfiguration. Meshes that reconfigure in magnetic fields and respond to external stimuli by reshaping could serve as active tissue scaffolds for cell cultures and soft robots mimicking creatures that live on the surface of water.}, number={4}, journal={ADVANCED MATERIALS TECHNOLOGIES}, publisher={Wiley}, author={Roh, Sangchul and Okello, Lilian B. and Golbasi, Nuran and Hankwitz, Jameson P. and Liu, Jessica A-C and Tracy, Joseph B. and Velev, Orlin D.}, year={2019}, month={Apr} }
 @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-+} }
 @article{roh_velev_2018, title={Nanomaterials Fabrication by Interfacial Templating and Capillary Engineering in Multiphasic Liquids}, volume={64}, ISSN={["1547-5905"]}, DOI={10.1002/aic.16348}, abstractNote={AIChE JournalVolume 64, Issue 10 p. 3558-3564 Perspective Nanomaterials Fabrication by Interfacial Templating and Capillary Engineering in Multiphasic Liquids Sangchul Roh, Sangchul Roh Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North CarolinaSearch for more papers by this authorOrlin D. Velev, Corresponding Author Orlin D. Velev odvelev@ncsu.edu Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North CarolinaCorrespondence concerning this article should be addressed to O. D. Velev at odvelev@ncsu.edu.Search for more papers by this author Sangchul Roh, Sangchul Roh Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North CarolinaSearch for more papers by this authorOrlin D. Velev, Corresponding Author Orlin D. Velev odvelev@ncsu.edu Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North CarolinaCorrespondence concerning this article should be addressed to O. D. Velev at odvelev@ncsu.edu.Search for more papers by this author First published: 27 June 2018 https://doi.org/10.1002/aic.16348Citations: 3 2017 Andreas Acrivos Award for Professional Progress in Chemical Engineering. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume64, Issue10October 2018Pages 3558-3564 RelatedInformation}, number={10}, journal={AICHE JOURNAL}, author={Roh, Sangchul and Velev, Orlin D.}, year={2018}, month={Oct}, pages={3558–3564} }
 @article{roh_parekh_bharti_stoyanov_velev_2017, title={3D Printing by Multiphase Silicone/Water Capillary Inks}, volume={29}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201701554}, abstractNote={3D printing of polymers is accomplished easily with thermoplastics as the extruded hot melt solidifies rapidly during the printing process. Printing with liquid polymer precursors is more challenging due to their longer curing times. One curable liquid polymer of specific interest is polydimethylsiloxane (PDMS). This study demonstrates a new efficient technique for 3D printing with PDMS by using a capillary suspension ink containing PDMS in the form of both precured microbeads and uncured liquid precursor, dispersed in water as continuous medium. The PDMS microbeads are held together in thixotropic granular paste by capillary attraction induced by the liquid precursor. These capillary suspensions possess high storage moduli and yield stresses that are needed for direct ink writing. They could be 3D printed and cured both in air and under water. The resulting PDMS structures are remarkably elastic, flexible, and extensible. As the ink is made of porous, biocompatible silicone that can be printed directly inside aqueous medium, it can be used in 3D printed biomedical products, or in applications such as direct printing of bioscaffolds on live tissue. This study demonstrates a number of examples using the high softness, elasticity, and resilience of these 3D printed structures.}, number={30}, journal={ADVANCED MATERIALS}, author={Roh, Sangchul and Parekh, Dishit P. and Bharti, Bhuvnesh and Stoyanov, Simeon D. and Velev, Orlin D.}, year={2017}, month={Aug} }