The effect of temperature on the formation of liesegang patterns of copper(II) chromate in polyacrylamide gels

Abstract

Liesegang patterns (LPs) are a subclass of periodic precipitation patterns that result in a reaction-diffusion (RD) without convection. Since their discovery, LPs have been studied to understand the effect of different parameters such as electric field, magnetic field, or concentration of ions/ gels and to elucidate the mechanism of pattern formation. LPs are visual "complex sums" of the chemical reactions forming the patterns, the diffusion of the chemicals, and the physical changes in the reaction environment. Different physical environments produce different patterns and therefore the patterns formed can be used to „sense‟ the physical environment, in which the patterns are formed – if the changing physical parameter of the environment is previously linked to the various patterns forming under these conditions. In this study, we aim to achieve an LP system (CuCl2(outer electrolyte)/K2CrO4(inner electrolyte) in polyacrylamide gel) that senses temperature by monitoring concurrent pattern formation. First, we illustrate the visual differences in LPs occurring at different temperatures. We unveil the changes in the diffusion of ions, the reaction rate, and the precipitation threshold inside the gel media for LP forming at different temperatures. LP's behaviors under different temperature ramp conditions leading to a difference in pattern evolution in terms of spacing, width, and time laws are shown. Finally, we show that temperature provides a degree of freedom towards material design through RD.