Density distribution for a dense hard-sphere gas in micro/nano-channels: Analytical and simulation results

We study the properties of a hard-sphere dense gas near the hard walls of micro and nano-channels. Analytical techniques, Monte Carlo (MC) methods and molecular dynamics (MD) simulation methods have been used to characterize the influence of the characteristic parameters such as number density, reduced density, width of the system and molecular diameter, on the equilibrium properties of the gas near the hard walls of micro and nano-channels. A mathematical model has been developed to characterize the density oscillations as the result of packing of molecules in case of a dense gas near the micro and nano-channels walls. The height and the position of the density oscillation peaks near the wall are characterized. These results are also confirmed by the MD and MC simulation results. Comparisons between MD and MC simulation results for particles having different diameter are also presented. For the same size of the particles and moderately dense gas, MC and MD results are similar, differences in the density profiles being limited only to the oscillatory region. For different particle sizes, MD and MC results are limited to a short distance near the wall for long size systems and moderately dense fluids. The effect of the boundary (particle size) on the simulation results is found to increase with g (reduced density) and it is very small in case of a dilute gas. For small g and small particle size (R) relative to the width of the system L, the height of the oscillation peaks is slowly increasing with R/L, and for high densities is always decreasing with R/L. The position of these peaks depends only on the size of the particles and when R is much smaller than L, it shows a small dependence on L. The deviations in the oscillatory region for the pure MC simulation results compared to pure MD simulation results are quantified, and more efficient hybrid MC–MD simulations are performed to reduce these deviations. 2006 Elsevier Inc. All rights reserved.