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Solvent mediated interactions close to fluid-fluid phase separation: microscopic treatment of bridging in a soft core fluid

A. J. Archer·R. Evans·R. Roth·M. Oettel
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Abstract

Using density functional theory we calculate the density profiles of a binary solvent adsorbed around a pair of big solute particles. All species interact via repulsive Gaussian potentials. The solvent exhibits fluid-fluid phase separation and for thermodynamic states near to coexistence the big particles can be surrounded by a thick adsorbed `wetting' film of the coexisting solvent phase. On reducing the separation between the two big particles we find there can be a `bridging' transition as the wetting films join to form a fluid bridge. The potential between the two big particles becomes long ranged and strongly attractive in the bridged configuration. Within our mean-field treatment the bridging transition results in a discontinuity in the solvent mediated force. We demonstrate that accounting for the phenomenon of bridging requires the presence of a non-zero bridge function in the correlations between the solute particles when our model fluid is described within a full mixture theory based upon the Ornstein-Zernike equations.

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A. J. Archer, R. Evans, R. Roth, M. Oettel. 2004-11-22. Solvent mediated interactions close to fluid-fluid phase separation: microscopic treatment of bridging in a soft core fluid. https://doi.org/10.1063/1.1855878

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