Turing patterns in a simple gel reactor

We introduce a very simple open two-dimensional gel reactor for studying chemical patterns that arise in reaction-diffusion systems. The reactor consists of a thin disk-shaped layer of polyvinyl alcohol gel with one face in direct contact with a well-stirred flow reactor containing reactants of the chlorite-iodide-malonic acid system; the other face of the gel is in contact with a piece of transparent plexiglass. We have used this reactor to study the transition from a uniform state to a hexagonal pattern; for other concentrations, striped patterns were observed. The wavelength of these structures is greater than the thickness of the gel layer, which indicates that the patterns are two-dimensional (a single layer). This reactor provides a promising new tool for studying chemical patterns since the diffusion time of reactants into and out of the gel can be made small compared to the total residence time in the stirred flow reactor. This feature facilitates the comparison between theory and experiment since the chemical concentrations leading to pattern formation are close to those in the stirred flow reactor and hence can be directly measured.