Belousov-Zhabotinsky's reaction

The Belousov-Zhabotinsky's(BZ) experiment (BZ) is a reaction that spontaneously exhibits colored patterns oscillations. In fact a whole ensemble of different chemical reactions is called BZ reaction, all them inspired in the original work. We concentrate ourselves in the main experimental facts of BZ.

Consider a metal-ion catalyzed oxidation of organic compounds (we shall not enter in the datails of the system compounds; more information, see C & H; Pomeau). The system is unstirred and in a steady-state. We can produce a small disturbance (i.e.: a localized perturbation) in the system propagating with constant velocity and constant shape, i.e., in the form of a circular pulse. If the steady-state is red, say, the pulse appear as a blue disturbance which decays back red behind the pulse. Matemathically, this means we have a bi-stable system, i.e., there are two solutions co-existing.

With a more complex initial condition, we can produce a lot of localized perturbations intercepting each other. Destruction of one by the others may be observed in this case (see figure 3). The phenomena observed here is analogous to vortex formation, where those with more energy destroy those with less energy.

Figure 3: Belousov-Zhabotinsky reaction (Vidal et al., 1986)

Even more interesting, is when a single expanding pulse is broken at a point (including another reagent, for instance): we see then spiral patterns (figure 4)

Figure 4: Belousov-Zhabotinsky reaction (Vidal et al., 1986, Cross & Hohenberg, 1993)