Refraction of chemical waves propagating in modified membranes

Abstract

Different possibilities to perform refraction experiments with chemical waves propagating in membranes modified with a fixed catalyst of the oscillatory Belousov–Zhabotinsky (BZ) reaction were investigated. Two methods to modify the velocity of chemical waves were developed. According to the first, barium sulfate was precipitated in certain regions of the modified membrane to decrease the wave velocity. The second method, which is more reproducible, applies barrier membranes, such as plastic foils or Nuclepore porous membranes, placed between the catalyst membrane and the reservoir of the other BZ reagents. Wave velocity maps calculated from the experiments show that the waves are slower in membrane regions which are separated from the reservoir by a barrier. When water evaporation from the membrane was allowed an inverse velocity map can be observed after some hours. A qualitative explanation of these observations is also presented. Finally, experiments made in an oxygen-free atmosphere prove that the wave refraction phenomena reported here are not caused by oxygen from the air.