Theory of nonionic hydrophobic solutes in mixture solvent: Solvent-mediated interaction and solute-induced phase separation

Abstract

We present a theory of nonionic solutes in a mixture solvent composed of water-like and alcohol-like species. First, we show the relationship among the solvation chemical potential, the partial volumes v, the Kirkwood-Buff integrals, the second osmotic virial coefficient, and the Gibbs transfer free energy. We examine how the solute density n is coupled to the solvent densities n and n in thermodynamics. In the limit of small compressibility, we show that the space-filling condition ∑ vn = 1 nearly holds for inhomogeneous densities n, where the concentration fluctuations of the solvent can give rise to a large solute-solute attractive interaction. We also derive a solute spinodal density n for solute-induced instability. Next, we examine gas-liquid and liquid-liquid phase transitions induced by a small amount of a solute using the Mansoori, Carnahan, Starling, and Leland model for hard-sphere mixtures [J. Chem. Phys. 54, 1523-1525 (1971)]. Here, we assume that the solvent is close to its gas-liquid coexistence and the solute interacts repulsively with the water-like species but attractively with the alcohol-like one. We calculate the binodal and spinodal curves in the phase diagrams and examine nucleation for these two phase transitions.

How antagonistic salts cause nematic ordering and behave like diblock copolymers

“…For most water-oil mixtures this value is much larger under normal conditions but can be expected to rapidly decrease to zero as the temperature approaches the critical point of demixing 27,28 . In a recent paper, Okamoto and Onuki have predicted a similar coupling as we observe of charge and order parameter between nonionic solutes in water-oil mixtures to explain the so-called Ouzoeffect 47 .…”

Theory of electrolytes including steric, attractive, and hydration interactions

“…For nonionic mixtures, the coefficients f ij are written in terms of thermodynamic derivatives (see Eq. ( 26) in our recent paper 67 ). Generally, f ij can be expressed as…”

“…For nonionic mixtures, v * i corresponds to v 0 2 − k B T κ w in Eq. (1) [48][49][50] and to v in 3 in our recent paper 67 . See also Eq.…”

“…( 12), the solvent-ion coupling arises from [f 12 n 2 (q) + f 13 n 3 (q)]n 1 (q) * . Thus, we introduce the deviation of the particle volume fraction 67 ,…”

“…It is a generalization of the Carnahan and Starling model of monodisperse hardspheres 64 . Using the MCSL model for neutral fluids, we studied small bubbles in water due to dissolved gases 65,66 and phase behavior in ternary mixtures 67 such as water-alcohol-hydrophobic solute 68 . In the latter, the second term in Eq.…”