Theory of phase separation in mixtures with lower critical solution temperature

Abstract

A thermodynamic theory of phase separation in mixtures possessing LCST is presented which incorporates (1) chemical equilibrium theory to account for cross association between solute and solvent, (2) Flory-Huggins theory for the difference of molecular volumes, and (3) NRTL equation for the interaction between molecules. The theoretical predictions of binodal curves over a wide temperature range are in good agreement with experimental findings in some binary aqueous solutions. The model can also reproduce the flat coexistence curves near the consolute points.

Thermodynamic modeling of the partitioning of biomolecules in aqueous two-phase systems using a modified Flory–Huggins equation

“…Experimental evidence of this behavior can be found, for instance, in Kjellander and Florin [18], where the solubility behavior of this polymer in water is attributed to this hydration effect. Other evidence of this hydration is presented in Goldstein [19], Karlström [20], Bordi et al [21], Yu and Nishiumi [22], Yu et al [23] and Dormidontova [24].…”

Structural changes of the molecular complexes of pyridines with water and demixing phenomena in aqueous solutions

“…1 This mechanism of demixing was widely used in the lattice models in order to reproduce close-loop phase diagrams of the aqueous solutions. [2][3][4][5][6] In accordance with this mechanism, lower critical solution temperature, unlike the upper one, is very sensitive to the details of the hydrogen bonding between unlike molecules. Therefore, variations of the H bonds between water and organic molecules must influence mainly on the lower critical temperature: Strengthening ͑weakening͒ of H bond causes increasing ͑decreasing͒ of T l without noticeable changes of T u .…”

“…Both these features contradict the existing model of demixing, connecting the lower critical point with the breakdown of the H bonds between solute and solvent molecules while the upper critical point is attributed exclusively to the entropy mixing. [1][2][3][4][5][6] The main purpose of the present paper is to find correspondence of the critical solution temperatures with the details of the intermolecular interaction in solution in order to propose a model of demixing, which is able to explain the main trends in the phase behavior of the aqueous mixtures with a closed-loop phase diagram. The main attention is concentrated on the temperature changes of the preferential structure of the pair complexes between unlike molecules.…”

The Chemical Thermodynamic Models for Calculating the Solvent Activity Coefficient of Semidiluted Aqueous and Nonaqueous Polymer Solutions in Vapor–Liquid Equilibrium

“…Their theory incorporates (1) chemical equilibrium theory to account cross solvation between solute and solvent, (2) Flory−Huggins theory for the difference of molecular volumes, and (3) NRTL theory for the interaction between molecules. 28 Also Yu et al applied this concept to phase separation in the aqueous solution of polymers. 29 In this study, based on Yu and Nishiumi's theory, new combinational models have been introduced and modified for solvent activity calculations in vapor−liquid equilibrium of some semidiluted binary polymer solutions at different temperatures.…”