Past experiments on Turing patterns have all been conducted using the chlorite-iodide-malonic acid (CIMA) reaction with Thiodène from Prolabo as an indicator. In this work two other indicators have been examined and found to yield Turing patterns similar to those obtained with Thiodène: soluble starch and poly(vinyl alcohol) (PVA). The present work shows that Thiodène is not simply a soluble starch, as previously assumed, but is probably made by mixing about 7% starch with 93% molten urea. To determine whether the indicators might also affect the chemical kinetics, the effect of the indicators was examined in batch studies of two CIMA systems: the minimal CIMA system (chlorine dioxide-iodine-malonic acid) and the CIMA-Cl system (chlorine dioxide-iodomalonic acid-chloride). It was found that starch and poly(vinyl alcohol) affect the dynamics of the minimal CIMA oscillator but they have no effect on the CIMA-Cl system. On the other hand, in the same or even larger weight/volume concentration glucose and 2-propanol had no effect on the minimal CIMA system. These findings prove that starch and poly(vinyl alcohol) participate exclusively in triiodide complex-forming reactions: they react with an enzyme-like selectivity. Thiodène, however, had an effect on the CIMA-Cl reaction because of its urea content.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry