Demixing, surface nematization, and competing adsorption in binary mixtures of hard rods and hard spheres under confinement

A molecular simulation study of binary mixtures of hard spherocylinders (HSCs) and hard spheres (HSs) confined between two structureless hard walls is presented. The principal aim of the work is to understand the effect of the presence of hard spheres on the entropically-driven surface nematization of the hard rod-like particles at the walls. The mixtures are studied using a constant normal-pressure Monte Carlo algorithm. The surface adsorption at different compositions of hard spheres is examined in detail. At moderate hard- sphere concentrations preferential adsorption of the spheres at the wall is found. However, at moderate to high pressure (density), we observe a crossover in the adsorption behaviour with nematic layers of the rods forming at the walls leading to a local demixing of the system. The presence of the spherical particles is seen to destabilize the surface nematization of the rods, and the degree of demixing increases on increasing the HS concentration.