Control of mosaic and turing patterns by light and electric field in the Methylene Blue sulfide-oxygen system

A variety of spatial patterns emerging in a system containing Methylene Blue, sulfide, and oxygen in a liquid layer and in a polyacrylamide gel are presented. We show the formation of long-lasting mosaic patterns arising from hydrodynamic instability and the transition from an irregular to a more regular, striped structure which occurs under the influence of an external electric field. We also demonstrate the formation of Turing patterns in a gel matrix. Here the gel plays an important role in the pattern formation process by slowing down the diffusion of the activator MB+. We present experiments showing that pattern formation can be influenced by visible light. An inhomogeneous illumination of the gel-sheet leads to selected regions of activity, which generates stripes instead of hexagons.