Density functional theory of inhomogeneous fluid mixture based on bridge function

Size selectivity in the confined ternary colloidal mixtures: the depletion in the competition

Based on classical density functional theory, we study the size selectivity for ternary colloidal mixtures in the presence of a Gauss barrier. The competition between the external potential and the depletion potential is also investigated. The effects of bulk fraction of each species, the size asymmetry, and the strength and width of the Gauss barrier on the selectivity of the big species are calculated and analyzed in detail. The results in different conditions of bulk fraction suggest that the larger the bulk fraction for the small species, the stronger selectivity of big particles. On the contrary, increase of bulk fraction for the big species leads to a reduction in selectivity. In addition, results under different conditions of size asymmetry suggest that the medium particles can also be selected by the Gauss barrier when they are sufficiently large in comparison to the small particles. We also demonstrate the effect of barrier geometry on the selectivity of the big species and the competition between the depletion and the external potential.

Multicomponent fluid of nonadditive hard spheres near a wall

A recently proposed rational-function approximation [Phys. Rev. E 84, 041201 (2011)] for the structural properties of nonadditive hard spheres is applied to evaluate analytically (in Laplace space) the local density profiles of multicomponent nonadditive hard-sphere mixtures near a planar nonadditive hard wall. The theory is assessed by comparison with NVT Monte Carlo simulations of binary mixtures with a size ratio 1:3 in three possible scenarios: a mixture with either positive or negative nonadditivity near an additive wall, an additive mixture with a nonadditive wall, and a nonadditive mixture with a nonadditive wall. It is observed that, while the theory tends to underestimate the local densities at contact (especially in the case of the big spheres) it captures very well the initial decay of the densities with increasing separation from the wall and the subsequent oscillations.

Multicomponent fluid of hard spheres near a wall

The rational function approximation method, density functional theory, and NVT Monte Carlo simulation are used to obtain the density profiles of multicomponent hard-sphere mixtures near a planar hard wall. Binary mixtures with a size ratio 1:3 in which both components occupy a similar volume are specifically examined. The results indicate that the present version of density functional theory yields an excellent overall performance. A reasonably accurate behavior of the rational function approximation method is also observed, except in the vicinity of the first minimum, where it may even predict unphysical negative values.

Inverse density-functional theory as an interpretive tool for measuring colloid-surface interactions in dense systems

Recent advances in optical microscopy, such as total internal reflection and confocal scanning laser techniques, now permit the direct three-dimensional tracking of large numbers of colloidal particles both near and far from interfaces. A novel application of this technology, currently being developed by one of the authors under the name of diffusing colloidal probe microscopy (DCPM), is to use colloidal particles as probes of the energetic characteristics of a surface. A major theoretical challenge in implementing DCPM is to obtain the potential energy of a single particle in the external field created by the surface, from the measured particle trajectories in a dense colloidal system. In this paper we develop an approach based on an inversion of density-functional theory (DFT), where we calculate the single-particle-surface potential from the experimentally measured equilibrium density profile in a nondilute colloidal fluid. The underlying DFT formulation is based on the recent work of Zhou and Ruckenstein [Zhou and Ruckenstein, J. Chem. Phys. 112, 8079 (2000)]. For model hard-sphere and Lennard-Jones systems, using Monte Carlo simulation to provide the "experimental" density profiles, we found that the inversion procedure reproduces the true particle-surface-potential energy to an accuracy within typical DCPM experimental limitations (approximately 0.1 kT) at low to moderate colloidal densities. The choice of DFT closures also significantly affects the accuracy.

Adsorption of Lennard-Jones fluid mixture in a planar slit: a perturbative density functional approach

A simple perturbative density functional approach is employed to investigate the adsorption behavior of a model Lennard-Jones fluid confined in a slitlike pore. Adsorption of one-component fluid as well as two-component fluid mixtures in varying pore sizes has been investigated. The results on the density profiles and the excess adsorption obtained from this theory are found to be in overall good agreement with the available computer simulation results. The results are also compared with the same from some recent weighted density based calculations.