Phase behavior and structure of model colloid-polymer mixtures confined between two parallel planar walls

Abstract

Using Gibbs ensemble Monte Carlo simulations and density functional theory we investigate the fluid-fluid demixing transition in inhomogeneous colloid-polymer mixtures confined between two parallel plates with separation distances between one and ten colloid diameters covering the complete range from quasi two-dimensional to bulk-like behavior. We use the Asakura-Oosawa-Vrij model in which colloid-colloid and colloid-polymer interactions are hard-sphere like, whilst the pair potential between polymers vanishes. Two different types of confinement induced by a pair of parallel walls are considered, namely either through two hard walls or through two semi-permeable walls that repel colloids but allow polymers to freely penetrate. For hard (semi-permeable) walls we find that the capillary binodal is shifted towards higher (lower) polymer fugacities and lower (higher) colloid fugacities as compared to the bulk binodal; this implies capillary condensation (evaporation) of the colloidal liquid phase in the slit. A macroscopic treatment is provided by a novel symmetric Kelvin equation for general binary mixtures, based on the proximity in chemical potentials of statepoints at capillary coexistence and the reference bulk coexistence. Results for capillary binodals compare well with those obtained from the classic version of the Kelvin equation due to Evans and Marini Bettolo Marconi [J. Chem. Phys. 86, 7138 (1987)], and are quantitatively accurate away from the fluid-fluid critical point, even at small wall separations. For hard walls the density profiles of polymers and colloids inside the slit display oscillations due to packing effects for all statepoints. For semi-permeable walls either similar structuring or flat profiles are found, depending on the statepoint considered.

15 pages, 13 figures

References in corpus (3)

• The fluid-fluid interface in a model colloid-polymer mixture: Application of grand canonical Monte Carlo to asymmetric binary mixtures
• Simulation and theory of fluid demixing and interfacial tension of mixtures of colloids and non-ideal polymers
• Accurate description of bulk and interfacial properties in colloid-polymer mixtures

Cited by in corpus (5)

• Statics and Dynamics of Colloid-Polymer Mixtures Near Their Critical Point of Phase Separation: A Computer Simulation Study of a Continuous AO Model
• Phase diagram and structure of colloid-polymer mixtures confined between walls
• Effect of excluded volume interactions on the interfacial properties of colloid-polymer mixtures
• Colloid-polymer mixtures in random porous media: Finite size scaling and connected versus disconnected susceptibilities
• From Capillary Condensation to Interface Localization Transitions in Colloid Polymer Mixtures Confined in Thin Film Geometry