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Correlation between inherent structures and phase separation mechanism in binary mixtures

Binary mixtures are known to phase separate via both nucleation and spinodal decomposition, depending on the initial composition and extent of the quench. Here we develop an energy landscape view of phase separation and non-ideality in binary mixtures by exploring their potential energy landscape (PEL) as functions of temperature and composition, by employing a molecular model that promotes structure breaking abilities of the solute-solvent parent binary liquid at low temperatures. PEL that provides the inherent structure (IS) of a system is obtained by removing the kinetic energy (including that of intermolecular vibrations). Broad Distribution of inherent structure energy demonstrates the larger role of entropy in stabilizing the parent liquid of the structure breaking type of binary mixtures. At high temperature, although the parent structure is homogenous, the corresponding inherent structure is found to be always phase separated, with a density pattern that exhibits marked correlation with the energy of inherent structure. Over broad range of intermediate inherent structure energy, bicontinuous phase separation prevails with interpenetrating stripes as signatures of spinodal decomposition. At low inherent structure energy, the structure is largely phase separated with one interface where as at high inherent structure energy, we find nucleation type growth. Interestingly, at low temperature, the average inherent structure energy (<EIS>) exhibits a drop with temperature which signals onset of crystallization in one of the phases while the other remains in the liquid state. The non-ideal composition dependence of viscosity is anti-correlated with average inherent structure energy.