Phase diagram and structure of colloid-polymer mixtures confined between walls

Abstract

The influence of confinement, due to flat parallel structureless walls, on phase separation in colloid-polymer mixtures, is investigated by means of grand-canonical Monte Carlo simulations. Ultra-thin films, with thicknesses between $D=3-10$ colloid diameters, are studied. The Asakura-Oosawa model [J. Chem. Phys. 22, 1255 (1954)] is used to describe the particle interactions. To simulate efficiently, a ``cluster move'' [J. Chem. Phys. 121, 3253 (2004)] is used in conjunction with successive umbrella sampling [J. Chem. Phys. 120, 10925 (2004)]. These techniques, when combined with finite size scaling, enable an accurate determination of the unmixing binodal. Our results show that the critical behavior of the confined mixture is described by ``effective'' critical exponents, which gradually develop from values near those of the two-dimensional Ising model, to those of the three-dimensional Ising model, as $D$ increases. The scaling predictions of Fisher and Nakanishi [J. Chem. Phys. 75, 5875 (1981)] for the shift of the critical point are compatible with our simulation results. Surprisingly, however, the colloid packing fraction at criticality approaches its bulk ($D\to \infty$) value non-monotonically, as $D$ is increased. Far from the critical point, our results are compatible with the simple Kelvin equation, implying a shift of order 1/D in the coexistence colloid chemical potential. We also present density profiles and pair distribution functions for a number of state points on the binodal, and the influence of the colloid-wall interaction is studied.

12 pages, 13 figures

References in corpus (5)

• Capillary Waves in a Colloid-Polymer Interface
• The fluid-fluid interface in a model colloid-polymer mixture: Application of grand canonical Monte Carlo to asymmetric binary mixtures
• Critical behavior of a colloid-polymer mixture confined between walls
• Phase behavior and structure of model colloid-polymer mixtures confined between two parallel planar walls
• Coexistence diameter in two-dimensional colloid-polymer mixtures

Cited by in corpus (5)

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• 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
• Phase separation of an asymmetric binary fluid mixture confined in a nanoscopic slit pore: Molecular-dynamics simulations
• Population inversion of a NAHS mixture adsorbed into a cylindrical pore