Spatiotemporal Control of Self-oscillating Gel by Uniformly Aligned Inorganic Nano Sheets

Abstract

A novel “self-oscillating” gel that exhibits an autonomous mechanical swelling–deswelling oscillation without any on–off switching of external stimuli has been developed since 1996. The basic chemical structure of the self-oscillating polymer is a copolymer of N-isopropylacrylamide (NIPAAm) and Ru(bpy)3 as a catalyst for the Belousov–Zhabotinsky (BZ) reaction. In response to the redox change of Ru(bpy)3 units, hydrophilicity and LCST of gel matrices change, which causes the swelling and deswelling of the gel networks. Unilamellar titania nanosheet (TiNS) is quite attractive, owing to its highly anisotropic shape and unique magnetic properties, where TiNSs in an aqueous dispersion magnetically align cofacially. Through in-situ polymerization, the aligned structure of TiNSs can be chemically locked in the hydrogel network. Based on this strategy, we fabricated an anisotropic self-oscillating hydrogel by hybridization of poly(NIPAAm) and Ru(bpy)3 units with uniformly aligned TiNSs. The as-prepared hydrogel showed autonomous swelling/deswelling behavior driven by BZ reaction, in a highly anisotropic manner.