Experimental pattern transitions in a Liesegang system

We experimentally found various patterns of precipitation in a lead iodide Liesegang system: periodic precipitation, continuous tree-like crystal aggreptes and periodic tree-like crystal aggregates. Gel and reactant concentrations are two major controlling factors. At high gel concentrations, Liesegan- band forms, whereas at low gel concentrations, tree-like crystal aggregates similar to diffusion-limited aggregation (DLA) develop in the entire system. At an intermediate act concentration, Liesegang band and tree-like crystal aggregates coexist. At lower reactant concentration, the periodic tree-like crystal aggreates tends to form. A simple scaling argument that the kinetics of bulk and surface nucleation plays an important role, is presented to understand the effect of gel concentration oil pattern transition. (C) 2003 Elsevier Science B.V. All rights reserved.