Monte Carlo simulation of hard chain–hard sphere mixtures in slitlike pores

Abstract

The structure of mixtures of hard chains (modeled as a pearl necklace of freely jointed hard spheres) and hard spheres in slitlike pores is studied using a canonical ensemble Monte Carlo method. Simulation results for the density profiles in pores with wall separations varying from two to ten hard sphere diameters are presented at overall volume fractions of 0.12 and 0.34, and the effect of pore size, chain concentration, and chain length on the structure of the chains is investigated. It is found that the chains are depleted at the wall at the lower density, but enhanced at the wall (relative to the center of the pore) at the higher density; this depletion increases as the chain length is increased. It is found that the enhancement of monomers and depletion/enhancement of chains at the wall becomes more marked as the pore size is increased. As all the pores we study are integer multiples of the bead diameter, we do not observe the oscillatory variation of the wall density with wall separation which is expected at high densities. The fluid is uniform in the middle of the larger pores, but is not uniform anywhere in the smaller pores. At the same total packing fraction, increasing the mole fraction of the monomers tends to remove the chains from the wall and also make the oscillations in the chain profile more pronounced. The density of end sites of the chain at the wall is higher than it is for middle sites. In the smaller pores, the chains are found to be flattened in the direction perpendicular to the walls; in large pores the fluid in the middle of the pore is essentially uniform.