Mesoscopic theory for inhomogeneous mixtures

Abstract

Mesoscopic density functional theory for inhomogeneous mixtures of sperical particles is developed in terms of mesoscopic volume fractions by a systematic coarse-graining procedure starting form microscopic theory. Approximate expressions for the correlation functions and for the grand potential are obtained for weak ordering on mesoscopic length scales. Stability analysis of the disordered phase is performed in mean-field approximation (MF) and beyond. MF shows existence of either a spinodal or a $\lambda$-surface on the volume-fractions - temperature phase diagram. Separation into homogeneous phases or formation of inhomogeneous distribution of particles occurs on the low-temperature side of the former or the latter surface respectively, depending on both the interaction potentials and the size ratios between particles of different species. Beyond MF the spinodal surface is shifted, and the instability at the $\lambda$-surface is suppressed by fluctuations. We interpret the $\lambda$-surface as a borderline between homogeneous and inhomogeneous (containing clusters or other aggregates) structure of the disordered phase. For two-component systems explicit expressions for the MF spinodal and $\lambda$-surfaces are derived. Examples of interaction potentials of simple form are analyzed in some detail, in order to identify conditions leading to inhomogeneous structures.

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• Correct scaling of the correlation length from a theory for concentrated electrolytes
• Effects of fluctuations on correlation functions in inhomogeneous mixtures
• Self-consistent theory for inhomogeneous systems with mesoscopic fluctuations
• Mesoscopic theory for systems with competing interactions near a confining wall
• Density functional theory for systems with mesoscopic inhomogeneities
• Correlation functions in mixtures with energetically favoured nearest-neighbours of different kind: a size-asymmetric case
• Onset of stripe order in classical fluids: Lessons from lattice-gas mixtures
• Mutual effect of charge- and number-density correlations in ionic liquids and concentrated electrolytes