PERTURBATION DENSITY-FUNCTIONAL THEORY FOR POLYATOMIC FLUIDS .3. APPLICATION TO HARD CHAIN MOLECULES IN SLITLIKE PORES

We present the first implementation of our density-functional theory for polyatomic molecules [J. Chem. Phys. 97, 9222 (1992); 99, 3950 (1993)] to investigate the structure of nonuniform polymer melts. In this theory, derived originally from Wertheim's perturbation theory of polymerization, the free energy of the nonuniform fluid is expressed as a functional of the full molecular distribution function and the excess contribution is calculated perturbatively over a reference fluid of monomers at the same temperature and singlet density as the real system. We compare theoretical predictions to simulations of freely jointed hard spheres confined between hard walls. We calculate the average and individual site density profiles, the bond orientation factor, and the adsorption isotherm. The theory is fairly accurate, though it tends to underestimate the depletion of chain sites near the walls at low densities and to overestimate the packing effects at high densities. It predicts very accurately, however, the density profile of chain ends.