Characterization of autonomously oscillating viscosity induced by swelling/deswelling oscillation of the microgels.

We report on autonomously oscillating viscosity in microgel dispersions induced by swelling/deswelling oscillations of the microgels. The microgels are composed of poly(N-isopropylacrylamide) in which ruthenium tris(2,2'-bipyridine), (Ru(bpy)(3)), a catalyst for the Belousov-Zhabotinsky (BZ) reaction, is covalently bonded to the polymer chain. At first, we measured hydrodynamic diameters of the microgels under the oxidized and reduced ruthenium states by dynamic light scattering. Then, measurements of viscosity in microgel dispersions under various microgel concentrations, ionic strengths, and temperatures were investigated. Next, the BZ reaction was carried out to measure the autonomously oscillating viscosity in the dispersions. In this study, the effect of the concentration of microgels, the concentration of the substrates for the BZ reaction, and the amount of Ru(bpy)(3) immobilized in microgels were investigated to authenticate how swelling/deswelling oscillations of the microgels were linked to the viscosity oscillations.