On the separation of nonadditive symmetric mixtures in nanoscopic slitlike pores: A simple model for racemic fluids

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.

Fundamental measure density functional theory for nonadditive hard-core mixtures: the one-dimensional case

We treat a one-dimensional binary mixture of hard-core particles that possess nonadditive diameters. For this model, a density functional theory is constructed following similar principles as an earlier extension of Rosenfeld's fundamental measure theory to three-dimensional nonadditive hard-sphere mixtures. The theory applies to arbitrary positive and moderate negative nonadditivity and reduces to Percus' exact functional in the additive case. Bulk direct correlation functions are obtained as functional derivatives of the excess free energy functional. Results for the partial pair correlation functions in bulk, as calculated via the Ornstein-Zernike route and using the direct correlation functions as input, show very good agreement with results from our Monte Carlo computer simulations of the mixture.

Chiral separation on a model adsorbent with periodic surface heterogeneity

Optimization of enantioselectivity in heterogeneous catalysis and chiral chromatography is a challenging task for the production of enantiopure chemicals. Enantioselective adsorbents usually consist of a surface with chiral receptors being either chiral molecules linked to the surface or chiral pockets formed by molecular templating of the surface. In both cases, the enantioselectivity is controlled mainly by the strength of the receptor-enantiomer interaction, such that one-to-one correspondence is usually preserved. The authors use Monte Carlo calculations to show that this steric requirement is not a necessary condition for the effective separation of chiral molecules. In particular, they propose a way in which a chiral surface can be constructed by a suitable spatial distribution of active sites for which the classical concept of a chiral receptor is no longer useful. Their calculations indicate that the effectiveness of the separation is affected mainly by the difference in shape of the adsorption energy distribution functions corresponding to the enantiomers.