Surface induced segregation of hard-sphere chain mixtures

Structure and segregation properties of a hard-sphere chain fluid dissolved in a polymeric solvent near a hard wall are investigated using the Percus-Yevick (PY) approximation for the associative Henderson-Abraham-Barker (HAB) equation. Both the polymer and the solvent are modeled as freely jointed hard-sphere chains of different lengths m(p) and m(s) and with different bead diameters d(p) and d(s). It is shown that there are two segregation factors: the bead diameter and the chain length difference, which cause structural features of the interface. It is determined that at low densities the segregation is mainly due to the chain-chain length difference, while the difference in the segment diameters is dominant at high densities. The structure is analyzed for various overall densities zeta(3) and polymer concentrations x(p). The partial density profiles as well as the segregation profiles are compared with Monte Carlo data to test the accuracy of the PY theory. (C) 1998 American Institute of Physics. [S0021-9606(98)51622-4].