Multiple iodide autocatalysis paths of chemo-hydrodynamical patterns in the Briggs–Rauscher reaction

Abstract

Autocatalytic feedback is often regarded as the core step for the chemo-hydrodynamical patterns in the nonlinear reaction system. The Briggs–Rauscher (BR) reaction shows sequential chemo-hydrodynamical patterns with three states, i.e. labyrinth, high iodine state, and rotating dendritic patterns. The short-lived labyrinth patterns, depending on [Mn²⁺]₀, the ratio of [CH₂(COOH)₂]₀ and [KIO₃]₀ and light intensities, result from iodide autocatalytic loop, which has three paths (involving Mn²⁺-induced radical reactions, the oxidation of iodomalonic compounds, and light-induced radical reactions, respectively). The high iodine state appears in a high ratio of [CH₂(COOH)₂]₀ and [KIO₃]₀, relating to the autocatalytic path involving the oxidation of iodomalonic compounds. The light-induced radical autocatalytic path can act as a convenient control parameter to modulate the patterns in the first stage by increasing the iodine radicals. The dendritic patterns in the third stage result from the Marangoni effect caused by the evaporation of the solutions and reactions between H₂O₂ and iodine-containing species, which is independent of [CH₂(COOH)₂]₀ and [Mn²⁺]₀. This work contributes to a better understanding of the complex spatiotemporal patterns in the chemo-hydrodynamical system.