Experimental realization and control of chemical turing-like patterns

An overview of spatial patterns emerging in a system containing methyleneblue, sulfide and molecular oxygen (MBO-system) in the presence of polyacry-lamide (PA) gel components is presented. In this so-called PA-MBO-System the gel plays an important role in the pattern formation process. In experiments conducted in a spatially twodimensional system we have found several different Turing-type structures such as hexagons, stripes and zig-zag patterns similar to those observed in the well known CIMA reaction. We examined the effect of an externally applied electrical field on the observed structures. The electrical field leads to the formation of striped patterns under conditions which favour the formation of hexagons in the absence of the field. The orientation of the stripes relative to the electrical filed vector depends on the intensity of the field: While a weak electrical field leads to stripes parallel to the field vector, higher field intensities lead to an orientation of the stripes perpendicular to it. In a spatially onedimensional system coexisting domains of stationary and Hopf-modes are formed under the influence of an electrical field. Moreover, we present experiments showing that pattern formation can be controlled by visible light. A selective illumination of the gel-sheet leads to distinct regions of activity which generates stripes instead of hexagons. Using illumination patterns of hexagonal symmetry and tunable wavelength we demonstrate spatial entrainment of the Turing-like patterns.