Dynamics of a complex diffusion-precipitation-re-dissolution Liesegang pattern

A complex behavior in a Liesegang system involving the precipitates Co(OH)2 and Ni(OH)2 is reported. Under a special choice of initial cation concentrations (Experiment III), a sequence of three band domains: BA (thin-medium), AA (medium-medium) and CA (thick-medium) repetitions is displayed, as opposed to a traditional periodic pattern observed over a range of Co2+ and Ni2+ concentrations (Experiments I and II). The dynamics involves diffusion, precipitation and re-dissolution, and is analyzed quantitatively. Oscillations in the % Co(OH)2 composition dominate the BA and AA regions, which later regularize into a monotonic and smooth decrease when the CA domain is reached.