Traveling Chemical Waves for Measuring Solute Diffusivity in Thermosensitive Poly(N-isopropylacrylamide) Gel

We have evaluated solute diffusivity in a gel by utilizing the Belousov−Zhabotinsky (BZ) reaction which is known as an oscillating reaction generating periodical redox changes of catalyst. The BZ reaction was induced in thermosensitive poly( N -isopropylacrylamide) (PNIPAAm) gel. By measurement of the velocity of an excited pulse of the oxidized catalyst (i.e., chemical wave) which propagates in the gel, the diffusivity of HBrO 2 as an intermediate in the gel was determined. The temperature dependence of the diffusivity was investigated for the PNIPAAm gel and bulk solution systems. Contrary to the bulk solution system, the diffusivity in the PNIPAAm gel decreased when increasing temperature. It was found that transport of solute through the gel was controlled by regulating the swelling properties of the gel. From a comparison with the diffusivity obtained from a conventional permeability measurement using a gel membrane, the new measuring method was found to be capable of almost same precision as the conventional method. The monitoring of the chemical wave would provide a novel experimental way for study of polymer gels.