Two dimensional chemical pattern formation in gels. Experiments and computer simulation

Precipitate forming chemical reactions have been studied in chemically cross-linked poly(vinyl-alcohol) gel layers and in thin silica films. One of the reactive components was incorporated into the gel, the other was allowed to diffuse into the film. This reaction-diffusion process resulted in patterns that were different in some respects from that of the regular Liesegang phenomena often occurring in such systems. Instead of stripes, tree-like precipitate structures have developed. Digital image analysis provided evidence that the tree-like structures involve a periodicity of the Liesegang type. Occurrence of this periodicity was found not only parallel but also perpendicular to the direction of the diffusion. Computer simulations were carried out in order to find possible mechanisms for these variants of the Liesegang phenomenon and to establish the influence of various factors on the chemical pattern formation involved in the model.