A face to remember: A photoimprinted image in a reactive microemulsion persisted for more than an hour. Such localized patterns in reaction–diffusion systems could find application in memory‐storage devices. The picture shows the image of a face immediately following illumination (a) and after 1 h (b). The area at the right shows the evolution of a spontaneous Turing pattern.

The Belousov-Zhabotinsky (BZ) reaction dispersed in water-in-oil aerosol OT (AOT) microemulsion has been studied at small radius R(d) of water nanodroplets (R(d) (nm) congruent with0.17omega,omega = [H(2)O][AOT] = 9). Stationary spotlike and labyrinthine Turing patterns are found close to the fully oxidized state. These patterns, islands of high concentration of the reduced state of the Ru(bpy)(3) (2+) catalyst, can coexist either with "black" reduction waves or, under other conditions, with the "white" oxidation waves usually observed in the BZ reaction. The experimental observations are analyzed with the aid of a new Oregonator-like model and qualitatively reproduced in computer simulations.

The effect of the iodide ions on the rate of the composite reactions of the oscillatory 103--S0,2--Fe-(CN)64-system suggests that the role of the iodate-iodide (Dushman) reaction is small in the composite reaction between 1 0 3 -and S03,-(positive feedback pathway), while it appears to be the main route for the 103--Fe(CN)64-reaction (negative feedback). It is found that oscillations in a semibatch reactor are preceded by a long nonoscillatory period during which the pH is about 5. Oscillations start without a nonoscillatory period if iodide is added to the reaction mixture at the beginning. These experiments confirm the role of the Dushman reaction in the negative feedback loop. No preoscillatory period is observed in the analogous Br03--S032--Fe(CN)64-oscillator in a semibatch reactor. It is also shown that ferricyanide is kinetically important as a consequence of its reaction with sulfite. Modeling of the behavior both in a semibatch configuration and in a CSTR with a set of composite reactions is carried out.

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