Striations in chemical reactions

Abstract

We present a theory of symmetry breaking in chemical reactions that takes into account both the kinetic aspects and the phase coexistence of the reacting species. Using a free energy functional that contains contributions from a concentration gradient in the reactants, simple criteria are derived for the conditions that lead to broken symmetries. Analytic expressions are obtained for the wavelength of the spatial structures and their characteristic time constants in terms of thermodynamic quantities. In the one dimensional case we also derive an expression for the interphase profile. We show that for a simple autocatalytic reaction it is possible to observe periodic patterns of chemical composition if the system is sufficiently far from phase coexistence equilibrium at a given time. Reactions with both positive and negative rate constants are analyzed in detail, and the role of nonlinearities in the time evolution of the system is discussed.