Solvent mediated interactions between model colloids and interfaces: A microscopic approach

TL;DR

This paper uses a microscopic density functional theory approach to calculate solvent-mediated effective potentials between colloids and interfaces in a binary solvent near phase separation, highlighting the impact of wetting films.

Contribution

It introduces a method to compute solvent-mediated potentials considering wetting films and phase preferences of colloids in a binary solvent system.

Findings

Wetting films significantly alter the effective potentials.

Different colloid preferences lead to distinct interaction profiles.

The approach captures the influence of phase behavior on colloid interactions.

Abstract

We determine the solvent mediated contribution to the effective potentials for model colloidal or nano- particles dispersed in a binary solvent that exhibits fluid-fluid phase separation. Using a simple density functional theory we calculate the density profiles of both solvent species in the presence of the `colloids', which are treated as external potentials, and determine the solvent mediated (SM) potentials. Specifically, we calculate SM potentials between (i) two colloids, (ii) a colloid and a planar fluid-fluid interface, and (iii) a colloid and a planar wall with an adsorbed wetting film. We consider three different types of colloidal particles: colloid A which prefers the bulk solvent phase rich in species 2, colloid C which prefers the solvent phase rich in species 1, and `neutral' colloid B which has no strong preference for either phase, i.e. the free energies to insert the colloid into either of the coexisting bulk phases are almost equal. When a colloid which has a preference for one of the two solvent phases is inserted into the disfavored phase at statepoints close to coexistence a thick adsorbed `wetting' film of the preferred phase may form around the colloids. The presence of the adsorbed film has a profound influence on the form of the SM potentials.