Interaction between macroparticles in Lennard-Jones fluids or in hard-sphere mixtures

We report results of numerical analyses on the surface (macroparticle) interactions in simple fluids. The singlet Ornstein-Zernike theories with hypernetted-chain closures are employed. With no (or very weak) attraction in the surface-fluid interaction u(MS), both the interaction phi(MM) and the force f(MM) between macroparticles in Lennard-Jones fluids are characterized by monotonically decreasing attraction. With increasing attraction in u(MS), however, phi(MM) and f(MM) become more oscillatory. The force between planar Lennard-Jones solids immersed in a Lennard-Jones fluid previously calculated by the grand canonical ensemble Monte Carlo simulation, which oscillates around zero with strong repulsion at small surface-to-surface separations, is well reproduced by our theoretical approach. The previously reported experimental observation that the addition of cyclohexane to octamethylcyclotetrasiloxane causes a reduction in the range of the solvation force is well demonstrated by our theoretical calculations on a simple binary mixture of hard spheres with different diameters. Similarly, the model reproduces the observation that at a sufficiently high mole fraction of cyclohexane there is less structure than in either of the pure liquids. (C) 1996 American Institute of Physics.