Model colloid polymer mixtures in porous matrices: density functional versus integral equations

Abstract

We test the accuracy of a recently proposed density functional (DF) for a fluid in contact with a porous matrix. The DF was constructed in the spirit of Rosenfeld's fundamental measure concept and was derived for general mixtures of hard core and ideal particles. The required double average over fluid and matrix configurations is performed explicitly. As an application we consider a model mixture where colloids and matrix particles are represented by hard spheres and polymers by ideal spheres. Integrating over the degrees of freedom of the polymers leads to a binary colloid-matrix system with effective Asakura-Oosawa pair potentials, which we treat with an integral-equation theory. We find that partial pair correlation functions from both theories are in good agreement with our computer simulation results, and that the theoretical results for the demixing binodals compare well, provided the polymer-to-colloid size ratio, and hence the effect of many-body interactions neglected in the effective model, is not too large. Consistently, we find that hard (ideal) matrix-polymer interactions induce capillary condensation (evaporation) of the colloidal liquid phase.

Fluid–fluid demixing curves for colloid–polymer mixtures in a random colloidal matrix

“…This work complements the results of Ref. [45], which instead studied the q dependence for a single value of R dis /R c , R dis /R c = 1, and of the disorder concentration.…”

“…We can compare our results with those obtained in Refs. [45,48]. By using densityfunctional methods, Ref.…”

“…AO colloid-polymer mixtures in a porous matrix have been studied in Refs. [45][46][47][48][49] by means of density-functional theory, integral equations, and…”

Isotropic-nematic transition of hard rods immersed in random sphere matrices

“…The conventional tool to study such quenched-annealed ͑QA͒ mixtures is via the replica trick, and a variety of liquid state integral equations have been carried over from equilibrium to QA models. Recently, a density functional theory ͑DFT͒ approach to such QA models was proposed 20,21 and demonstrated to give good account of hard sphere correlations, 20 capillary condensation and evaporation, 22,23 surface behavior of hard spheres, 24 freezing in a lattice model, 25 and the structure of hard spheres immersed in random fiber networks. 26 In this work we combine the tools developed in Refs.…”

First-principles derivation of density-functional formalism for quenched-annealed systems

“…In this line are the works by Schmidt and collaborators [8,12,14], which make use of the constructing principle of fundamental measure theory [9,10,11,13], namely the exact result for a 0D cavity (a cavity which can hold at most either a fluid or a matrix particle)…”