Density functional theory for nonuniform polymer melts: Based on the universality of the free energy density functional

A density functional theory is proposed for nonuniform freely jointed tange ntial hard sphere polymer melts in which the bonding interaction is treated on the basis of the properties of the Dirac delta -function, thus avoiding the use of the single chain simulation in the theory. The excess free ener gy is treated by making use of the universality of the free energy density functional and the Verlet-modified (VM) bridge function. To proceed numeric ally, one of the input parameters, the second-order direct correlation func tion of a uniform polymer melt is obtained by solving numerically the Polym er-RISM integral equation with the Percus-Yevick (PY) closure. The predicti ons of the present theory for the site density distribution, the partition coefficient and the adsorption isotherm, near a hard wall or between two ha rd walls are compared with computer simulation results and with those of pr evious theories. Comparison indicates that the present approach is more acc urate than the previous integral equation theory and the most accurate Mont e Carlo density functional theories. The predicted oscillations of the medi um-induced force between trio hard walls immersed in polymer melts are cons istent with the experimental results available in the literature.