Chemical waves in self-oscillating gels
The behaviors of a poly(N-isopropyl acrylamide) (PNIPA) gel coupled with the Belousov-Zhabotinsky (BZ) reaction has been investigated as a function of temperature and catalyst concentration. In this type of gel, the chemical oscillation in the BZ reaction induces periodic and autonomous swelling-shrinking volume changes of the gel, and conversely a volume change of the PNIPA gel affects the propagation of the chemical wave. Our attention was focused on the effects of mechanical changes on the chemical wave by utilizing the thermally driven volume phase transition of the gel. Both the velocity and the frequency of the chemical wave increased with increasing temperature, and abruptly decreased at the volume transition temperature of the gel, T(c). The diffusion of HBrO2, which is essential for wave propagation, was hindered with increasing temperature. The diffusion of HBrO2 through the gel network in the low temperature region was explained in the same way as a simple diffusion of inactive molecules through a restricted environment.