Chemical freezing of phase separation in immiscible binary mixtures

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Abstract
We discuss the thermodynamic and kinetic conditions under which chemical reactions may prevent the coarsening terminating spinodal decomposition and freeze the unmixing of binary mixtures at some early, pattern forming, stage of evolution. Under very general conditions, we establish that (i) this pattern freezing phenomenon can only occur in nonequilibrium systems the level of dissipation of which exceeds a finite, nonzero threshold value; (ii) at least two independent chemical processes must take place; (iii) chemistry must be destabilizing, which requires that at least one of these processes must be autocatalytic; (iv) pattern formation is possible even outside of the spinodal region, i.e., without involving a phase separation phenomenon, in unsymmetrical mixtures where the potential energies between pairs of identical particles are sufficiently different. This latter condition replaces for nonideal chemically reacting binary mixtures the unequal diffusion coefficients condition which governs the appearance of Turing patterns in the classical reaction-diffusion theory.