Size-dependent switching of the spatiotemporal structure between a traveling wave and global rhythm

The spatiotemporal chemical structure in the Belousov-Zhabotinsky (BZ) reaction was studied using spherical beads of ion-exchange resin doped with ferroin by changing the size of the beads. Above an upper critical size (ca. 0.8 nm in diameter), chemical waves emerge and propagate on the surface of a bead by forming a target or spiral pattern. Below a lower critical size (ca. 0.62 mm in diameter); uniform global oscillation over the entire bead is observed; i.e., no traveling wave is observed. Between these upper and lower critical sizes, the reaction is bistable with regard to the two different modes, i.e., uniform oscillation and a traveling wave. This experimental trend is discussed in terms of competition between the growth rate and diffusion rate of the activator.