Pattern formation induced by ion-selective surfaces: Models and simulations

Abstract

Simple inorganic reactions in gels, such as NaOH + CuCl(2), NaOH + AgNO(3), and CuCl(2) + K(3)[Fe(CN)(6)], can yield to various precipitation patterns. The first compound penetrates in a hydrogel by diffusion, and reacts with the second compound homogenized in the gel. The precipitate patterns formed in these reactions have got two kinds of bordering surfaces. Recent experimental results suggested that one of these surfaces has an ion-selective (semipermeable) character: It restrains the diffusion of the reacting ion contained by the reactant that diffuses into the gel. In this paper, we built the above experimental observation into a reaction-diffusion cellular-automata model of the pattern formation. Computer simulations showed that the model is able to reproduce the basic building elements of the patterns.