Highly porous, emulsion-templated, zwitterionic hydrogels: amplified and accelerated uptakes with enhanced environmental sensitivity†
A series of highly porous zwitterionic hydrogel polyHIPEs (Z-HG-PHs) were synthesized within oil-in-water high internal phase emulsions (HIPEs) from N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethylammonium betaine and crosslinked with N,N′-methylenebisacrylamide. The Z-HG-PHs exhibited an anti-polyelectrolyte effect, with the uptake of aqueous NaCl solutions increasing with increasing NaCl concentration, and unusually, the uptake of urine was significantly higher than that of water. In addition, the high chemical stability of the Z-HG-PHs enabled the uptake and storage of a 6 M HCl solution. The Z-HG-PHs exhibited dual-pH sensitive uptakes, with the uptake decreasing from pH 2 to 7 and then increasing from pH 7 to 10, and the uptake increased with increasing temperature. The emulsion-templated structure of the Z-HG-PHs amplified and accelerated the uptake and enhanced the sensitivity to the environment through hydrogel-swelling-driven void expansion. Emulsion templating provides a novel route not only to amplify and accelerate the uptake, but also to enhance the environmental sensitivity.