Artigo Revisado por pares

Spontaneous pattern formation in precipitating systems

1978; American Institute of Physics; Volume: 69; Issue: 1 Linguagem: Inglês

10.1063/1.436406

ISSN

1520-9032

Autores

D. Feinn, P. Ortoleva, W. Scalf, Slawa Schmidt, M. Wolff,

Tópico(s)

Coastal wetland ecosystem dynamics

Resumo

A series of new experiments on patterned precipitation are presented which clearly show the symmetry breaking aspects of these systems. In one configuration a system consisting of lead iodide, water, and agar is shown to display a symmetry breaking instability in precipitation from a supersaturated gel solution prepared by supercooling. In another configuration the system is maintained out of equilibrium for long times by feeding a gel layer from opposite sides with lead nitrate and potassium iodide (or similar pairs of precipitating reactants). In this latter experiment the precipitation in the plane of the reaction gel layer is shown to form spontaneous patterning, breaking the symmetry imposed by the uniform baths of lead nitrate and potassium iodide. The patterns range from mosaic to speckled in nature depending on the concentrations of the reactants and the thickness of the gel layers. A new mechanism for patterned precipitation is proposed which is based on a consideration of the surface tension of the precipitate particles. Feedback in this view is provided because the larger particles may grow at the expense of smaller ones. The mechanism is not inconsistent with the Ostwald–Prager theory of Liesengang rings but unlike the latter can explain pattern formation in the absence of imposed gradients. The present theory may also be used to explain secondary bands in the classic Liesengang experiments as well as several types of spontaneous center patterns and a divergence in the coherence or pattern length found in the experiments presented here.

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