MONTE-CARLO SIMULATION OF POLYMERS CONFINED BETWEEN FLAT PLATES

The behavior of polymers (modeled as a pearl necklace of n = 20 freely jointed hard spheres) between hard walls is studied by using a canonical ensemble Monte Carlo method. Simulation results for the density profiles and configurational properties are presented for wall separations varying from 4 to 16 hard sphere diameters and for volume fractions of 0.1, 0.2, and 0.3. 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. The density of end sites of the chain at the wall is higher than it is for middle sites. Near the wall the chains are found to be flattened against the wall; in the large pore the fluid in the middle of the pore is uniform. In the bulk region, the distribution of sites about the center of mass is Gaussian; near the wall it is asymmetric and sharply peaked. In the smallest pore the chains are almost two dimensional. The force on the walls as a function of wall separation is calculated by using a superposition approximation to obtain the density profile for a fluid in small pores from the density profile for a fluid in a large pore at the same chemical potential. At high densities the force is an oscillatory function of wall separation with a period of oscillation of about one bead diameter, but at low densities it is monotonic and attractive. © 1990, American Chemical Society. All rights reserved.