Morphology, particle size distribution, and composition in one- and two-salt metal oxinate Liesegang patterns

Precipitate systems consist of particles of various sizes distributed in space. The determination of the particle size distribution (PSD) in a precipitate allows a better understanding of the spatio-temporal dynamics of such a system. The Liesegang method of growing precipitates in gels slows down the kinetics of precipitation to a diffusion-controlled limit and yields exotic patterns of parallel salt bands. This promotes the possibility of measuring the PSD, especially when bands with well-dispersed particles in space are obtained. Such an experiment was realized in our laboratory on cobalt(II) oxinate yielding appropriate patterns with exactly the desired features. We here attempt to improve and quantify these experiments, to measure the PSD using different analysis methods. The measurements are performed via two routes: in the laboratory under the microscope and by image analysis of 2D pictures of the various bands. The two methods show a good qualitative agreement in that the trends are almost perfectly reproduced. The band morphology is studied notably as a function of initial supersaturation, and novel features related to particle size and number density are observed. Two-salt metal oxinate patterns are prepared and analyzed.