Precipitation patterns with polygonal boundaries between electrolytes

Abstract

Two-dimensional Liesegang patterns formed when the boundary between electrolytes is polygonal display a variety of patterns, such as dislocations (radial alleys of gaps), branches (anastomoses) and spirals, many of which can be found in nature. Each vertex of the polygon can produce a pair of dislocation lines or branch lines. The effect caused by a vertex decreases with the number of vertices. Double-armed spirals are observed in experiments with a pentagonal boundary. Hexagons, which begin to approach smooth circular boundaries, do not give rise to dislocations, but instead yield concentric precipitation rings. A simple model of nucleation growth enables us to simulate dislocations and spirals consistent with those seen in our experiments.