Suspensions of rod-like colloids and a depleting agent under confinement

Abstract

We present a computer simulation study of suspensions of rod-like colloids and a depletantin confinement to a slit-pore. Mixtures of hard spherocylinders and ideal spheres werestudied by means of Monte Carlo simulations in the grand canonical ensemble. By use offinite size scaling analysis we determined the critical behaviour. In order to overcome largebarriers in the free energy we applied the successive umbrella sampling method(Virnau and Müller 2004 J. Chem. Phys. 120 10925). We find that, under confinement,the critical point of gas–liquid demixing shifts to higher concentrations of rodsand smaller concentrations of spheres due to the formation of an orientationallyordered surface film. If the separation between the walls becomes very small, thecritical point is shifted back to smaller concentrations of rods because the surfacefilm breaks up. In particular, we present a method for determining the wettingbehaviour from an analysis of the distribution of particle concentration. For large wallseparations we find wetting near the critical point consistent with the Cahn argument.