Chemomechanical Motion of a Self-Oscillating Gel in a Protic Ionic Liquid
Graphical Abstract
An autonomous swelling-deswelling oscillation of polymer gels was achieved in a hydrated protic ionic liquid (PIL) as a proton source for the Belousov–Zhabotinsky (BZ) reaction. The PIL acts as a medium for the BZ reaction and is a promising material for developing self-oscillating gels under milder conditions.
Abstract
An autonomous swelling–deswelling oscillation of polymer gels in a hydrated protic ionic liquid (PIL) as a proton source for the Belousov–Zhabotinsky (BZ) reaction is presented. Methylammonium hydrogen sulfate ([maH+][HSO4−]) was employed as the PIL because it provides stable redox oscillation in the BZ reaction. Due to the significantly higher pKa for [maH+][HSO4−] than those for conventional proton sources for the BZ reaction, chemomechanical oscillation can be expected under weaker acidic conditions. The self-oscillating polymer was designed as a ternary random copolymer of N-isopropylacrylamide, N-(3-aminopropyl)methacrylamide, and the Ru(bpy)3 moiety as a catalyst for the BZ reaction. The copolymer exhibited spontaneous soluble–insoluble oscillation in hydrated [maH+][HSO4−] containing NaBrO3 and malonic acid. Macroscopic swelling–deswelling oscillation of the porous bulk gel prepared by covalently connecting microgel particles was also observed.
