Chemical Waves in Mesoporous Media

T. Amemiya, M. Nakaiwa, T. Ohmori, and T. Yamaguchi
[Physica D, Vol.84, pp.103-111, 1995]

Chemical waves in the Belousov-Zhabotinsky (BZ) reaction were investigated in mesoporous glass (vycor 7930). Some characteristics such as wavelengths or pattern sizes, periods and velocities of chemical waves have been found in the glass systems. The velocity of the waves in the vycors glass (pore diameter ~40 Å, ca. 10 times larger than the reacting molecules) was about 1/3 of that in aqueous systems. A microscopic model for the wave propagation in mesoporous glass is presented. The reduced velocity of the chemical waves is explained in terms of the reaction and diffusion in a fractal-like network of narrow channels. Porous glass has been found to be a useful heterogeneous medium for studying chemical patterns under open conditions.

Fig. 1. Velocity of chemical waves vs. the square root of the product of proton and bromate concentrations. Absorbance of the Ru(bpy)²⁺₃ -immobilized vycor glass at 460 nm was 0.51 (ca. 4.2 mM in the glass). The ratio of the wave velocity in vycor glass to that in aqueous solutions (nu_g/nu_s) was in the range from 0.27 to 0.29. The ratio of the two slopes (nu_g.slope/nu_s.slope) was 0.24.

Fig. 2. Schematic representation of mesoporous glass as a interconnected network (a) of a cylindrical channel (b). The diameter of the vycor glass was ca. 40 Å, and was ca. 10 times larger than that of reacting molecules.