In-phase synchronization of chemical and mechanical oscillations in self-oscillating gels

A novel gel which undergoes an autonomic and periodical swelling-deswelling oscillation has been prepared by the copolymerization of N-isopropylacrylamide (NIPAAm) with ruthenium tris(2,2'-bipyridine) (Ru(bpy)(3)) as a catalyst for the Belousov-Zhabotinsky (BZ) reaction, which is known as an oscillating reaction accompanying a rhythmical change in the redox potential. The swelling-deswelling cycle of a miniature cubic poly(NIPAAm-co-Ru(bpy)(3)) gel was found to be synchronized with the chemical oscillation without a phase difference. The oscillating profiles of the swelling-deswelling changes as well as the redox changes were studied as a function of the substrate concentrations by using an image-processing method. Both period and amplitude of chemical oscillation varied depending on the substrate concentration. This variation led to a change in the swelling-deswelling oscillation: i.e., the swelling-deswelling amplitude increased with an increase in the period and amplitude of the redox changes. In the synchronization process, a feedback mechanism from mechanical to chemical oscillation was also suggested. The change in gel size with ca. 20% to the initial size was obtained as the maximum value. The swelling-deswelling amplitude of the gel is controllable by changing the initial concentration of substrates or the content of immobilized Ru(bpy)3 catalyst within the gel.