Periodically Precipitating Patterns of AgCl through Reaction-Diffusion in Agar Gel: Role of Supersaturation

Abstract

The bottom up approach of formation of periodic precipitation (PP) through reaction diffusion (RD) is emerging as a novel method for the synthesis of mono-dispersed micro and nano-particles. In PP, one of the reactants (invading) meets the other (stationary) immobilized into the gel. The diffusional flux of the invading electrolyte can be controlled by varying its concentration and the geometry of the experimental setup which in turn can control the extent of supersaturation at band site. In the present paper, periodic bands of AgCl were obtained using conventional 2D Liesegang experimental setup by varying the reactant concentrations. By evaluating the experimental value of diffusion coefficients, the supersaturation at each precipitation band was calculated. It was observed that, the value of supersaturation was the maximum at first band indicating the re-dissolution of the precipitation product and then found to decrease successive with band number. As supersaturation is inversely related to particle size, bigger size particles were formed in the last band. This observation was confirmed by optical micrograph images of the particles in the bands.