Structure formation during precipitation reaction in gels - New Liesegang patterns

The paper reports on an investigation carried out into one- to three-dimensional Liesegang systems (test tube arrangement) composed of different concentrations of lead nitrate in Agar gel with either potassium iodide or potassium dichromate as the precipitation reagent. A rich variety of different structure formations, including screw formations of the weakly soluble reaction product is documented. Measurements of the progression of the precipitation front show a dependence of the diffusion path on time that which deviates from the Einstein-Smoluchowski root mean square displacement. The measured exponent n of the displacement x(n)=f(t) is discussed in detail and interpreted as the dynamic dimension d(w) of the diffusion through the fractal medium of the gel, the backbone dimension of which could be estimated. A cellular automaton model is used to describe the DLA cluster formation of the precipitate as well as the geometrical shape of the Liesegang patterns.