Polydisperse hard spheres at a hard wall

Abstract

The structural properties of polydisperse hard spheres in the presence of a hard wall are investigated via Monte Carlo simulation and density functional theory (DFT). Attention is focussed on the local density distribution $\rho (\sigma ,z)$, measuring the number density of particles of diameter $\sigma$ at a distance $z$ from the wall. The form of $\rho (\sigma ,z)$ is obtained for bulk volume fractions ${\eta }_b=0.2$ and ${\eta }_b=0.4$ for two choices of the bulk parent distribution: a top-hat form, which we study for degrees of polydispersity $\delta =11.5$ and $\delta =40.4$, and a truncated Schulz form having $\delta =40.7$. Excellent overall agreement is found between the DFT and simulation results, particularly at ${\eta }_b=0.2$. A detailed analysis of $\rho (\sigma ,z)$ confirms the presence of oscillatory size segregation effects observed in a previous DFT study (Pagonabarraga {\em et al.}, Phys. Rev. Lett. {\bf 84}, 911 (2000)). For large $\delta$, the character of these oscillation is observed to depend strongly on the shape of the parent distribution. In the vicinity of the wall, attractive $\sigma$-dependent depletion interactions are found to greatly enhance the density of the largest particles. The local degree of polydispersity $\delta (z)$ is suppressed in this region, while further from the wall it exhibits oscillations.

12 pages revtex

References in corpus (5)

• Equilibrium phase behavior of polydisperse hard spheres
• Simplified Onsager theory for isotropic-nematic phase equilibria of length polydisperse hard rods
• Phase equilibria and fractionation in a polydisperse fluid
• A non-equilibrium Monte Carlo approach to potential refinement in inverse problems
• Liquid-gas coexistence and critical point shifts in size-disperse fluids

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• Test of a universality ansatz for the contact values of the radial distribution functions of hard-sphere mixtures near a hard wall
• Smectic and columnar ordering in length-polydisperse fluids of parallel hard cylinders
• Liquid-vapor interface of a polydisperse fluid
• Freezing line of polydisperse hard spheres via direct-coexistence simulations