Colloid-polymer mixtures under slit confinement.

Abstract

We report a NVT molecular dynamic study of colloid-polymer mixtures under slit confinement. For this purpose, we are employing the Asakura-Oosawa model for studying colloidal particles, polymer coils, and hard walls as the external confining field. The colloid-polymer size ratio, q, is varied in the range 1⩾q⩾0.4 and the confinement distance, H, in 10σc⩾H⩾3σc, σc being the colloidal diameter. Vapor-liquid coexistence properties are assessed, from which phase diagrams are built. The obtained data fulfill the corresponding states law for a constant H when q is varied. The shift of the polymer and colloidal chemical potentials of coexistence follows a linear relationship with (H-σc)-1 for H≳4σc. The confined vapor-liquid interfaces can be fitted with a semicircular line of curvature (H-σc)-1, from which the contact angle can be obtained. We observe complete wetting of the confining walls for reservoir polymer concentrations above and close to the critical value, and partial wetting for reservoir polymer concentrations above and far from it.