Surfactant-free fabrication of pNIPAAm microgels in microfluidic devices
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EARLY CAREER SCHOLARS IN MATERIALS SCIENCE 2019 Surfactant-free fabrication of pNIPAAm microgels in microfluidic devices Mutian Hua, Yingjie Du, Jiaqi Song, Mo Sun, and Ximin Hea) Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90024, USA (Received 1 June 2018; accepted 4 September 2018)
Conventional pNIPAAm microgel synthesis utilizes surfactants to suspend pre-gel droplets in the immiscible continuous phase due to the slow polymerization required for synthesizing pNIPAAm in aqueous solvent. To improve the fabrication process and to eliminate the effects of surfactant on microgel quality, a surfactant-free and water-free method was developed. Rapid polymerization of high-quality microgels was achieved in a single-channel microfluidic device to help maintain the integrity of gel particles without the addition of surfactants. The droplet generation mechanism and the effect of flow rate of the two in-going immiscible fluid on the geometry of the produced microgels were studied. The produced microgels have low polydispersity with a dispersity index of 6.4%. The pNIPAAm hydrogels fabricated in the DMSO solvent has smaller pore size and more uniform microstructure compared to that synthesized in water. The fabricated pNIPAAm microgels show a sharp volume phase transition at ;32 °C and high deswelling/swelling rate. Ximin He is an assistant professor of Materials Science and Engineering at University of California, Los Angeles, and Faculty of California Nanosystems Institute (CNSI). Dr. He was postdoctoral research fellow in Wyss Institute of Bioinspired Engineering and School of Engineering and Applied Science with Professor Joanna Aizenberg at Harvard University. Dr. He received her Ph.D. in Chemistry in the fields of Nanoscience and Organic Optoelectronics from University of Cambridge, Melville Laboratory for Polymer Synthesis, Cavendish Laboratory and Nanoscience Center. Dr. He’s research focuses on biologically inspired functional smart materials, chemical and biological sensors, actuators with broad applications in materials science, biomedicine, environment, and energy. Dr. He is the recipient of the NSF CAREER award, AFOSR Young Investigator Program award, Harvard Postdoctoral Award for Professional Development, Gates Cambridge Scholarship, U.K. Overseas Research Scholarship, the Government Award for National Outstanding Students, and U.K. National Excellent Young Scientist Award. Ximin He
I. INTRODUCTION
Responsive microgels are crosslinked micron/submicron sized polymeric particles that can swell or deswell in response to external stimuli.1 The osmosis nature of hydrogels’ volume changing mechanism makes microgels extremely advantageous in achieving fast (de)swelling rate due to their reduced diffusion distance and increased surface area compared to bulk gels. Due to their unique thermal responsive behaviors, poly(N-isopropylacrylamide) (pNIPAAm) microgels hold exceptional interest in broad research areas such as environmental, biomedical, and energy
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