Solvent mediated forces in critical fluids

Abstract

The effective interaction between two planar walls immersed in a fluid is investigated by use of Density Functional Theory in the super-critical region of the phase diagram. A hard core Yukawa model of fluid is studied with special attention to the critical region. To achieve this goal a new formulation of the Weighted Density Approximation coupled with the Hierarchical Reference Theory, able to deal with critical long wavelength fluctuations, is put forward and compared with other approaches. The effective interaction between the walls is seen to change character on lowering the temperature: The strong oscillations induced by layering of the molecules, typical of the depletion mechanism in hard core systems, are gradually smoothed and, close to the critical point, a long range attractive tail emerges leading to a scaling form which agrees with the expectations based on the critical Casimir effect. Strong corrections to scaling are seen to affect the results up to very small reduced temperatures. By use of Derjaguin approximation, this investigation has natural implications for the aggregation of colloidal particles in critical solvents.

15 pages, 16 figures

References in corpus (5)

• Universal scaling functions of critical Casimir forces obtained by Monte Carlo simulations
• Monte Carlo simulation results for critical Casimir forces
• Off-critical Casimir effect in Ising Slabs with Symmetric Boundary Conditions in d=3
• Critical Casimir forces and colloidal aggregation: A numerical study
• Tuning effective interactions close to the critical point in colloidal suspensions

Cited by in corpus (2)

• Collective behavior of colloids due to critical Casimir interactions
• Sign change in the net force in sphere-plate and sphere-sphere systems immersed in nonpolar critical fluid due to the interplay between the critical Casimir and dispersion van der Waals forces