Abstract
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.
Highlights
Responsive microgels are crosslinked micron/submicron sized polymeric particles that can swell or deswell in response to external stimuli.[1]
Bulk pNIPAAm hydrogels were synthesized in water and DMSO to study the solvent effect on hydrogel microstructures. 20% NIPAAm 1 1% Bis 1 1% ammonia persulfate (APS) in water and 20% NIPAAm 1 1% Bis 1 1% Daracure 1173 in DMSO were used as the pre-gel solution. 500 lL of pre-gel solutions were pipetted into a 2 mL glass vial, respectively
Since pNIPAAm undergoes unique volume phase transition around 32 °C in aqueous environment, localized polymerization heat may lead to the insolubility or even precipitation of NIPAAm monomers out of the aqueous phase during the polymerization of pNIPAAm hydrogel
Summary
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 fields. Detailed characterization of the synthesized pNIPAAm hydrogels were conducted to investigate the influence of solvent and flow rate on their microstructure, geometry, and thermal properties
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