New indicators for visualizing pattern formation in uncatalyzed bromate oscillatory systems

Abstract

Many uncatalyzed bromate oscillators (UBO's) undergo oscillations in electrochemical potential without any observable color change in a closed, stirred (batch) system. We have investigated the effects of adding a wide variety of redox indicators, including diphenylamine derivatives, a/o dyestuffs, triphenylmethane derivatives, diimine chelate complexes, and methylene blue to UBO's. We find that in many cases the indicators make the batch oscillations strikingly visible and also allow observation of spatial pattern formation (concentric rings and spirals) in a thin, unstirred layer of solution. In some systems, the indicators act merely to make visible changes in redox potential, while in others they play an active role in the chemistry, and added indicator can lengthen the duration of oscillations or regenerate oscillations or patterns once this behavior has ceased.