Simple inorganic reactions, coupled with diffusion, are able to produce regular patterns of characteristic length scales of 10 µm. Solutions of CuCl2 or AgNO3 are homogenised in poly(vinyl)alcohol gel, and NaOH is allowed to diffuse into the gel. Reaction of the NaOH solution with the electrolyte present in the gel forms precipitates, which can show several types of primary (macroscopic) patterns, including spirals and target-like patterns. Depending on the velocity of the reaction front, the colloidal precipitate developed in this chemical reaction can yield a microscopic structure consisting of ordered sheets of particles. Conditions of formation and characterisation of the secondary (microscopic) patterns are presented. Emergence and disappearance of defects in these structures are also investigated. Possible theoretical explanation and technological applications of the microscopic patterns are discussed.
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