LOCAL-STRUCTURE OF SEMIFLEXIBLE POLYMER MELTS

Polymer RISM (reference interaction site model) theory is used to examine the intermolecular radial distribution function and isothermal compressibility of semiflexible polymer melts. Chains are modeled as a series of linked, hard sites with a local bending energy proportional to the cosine of the bond angle. Chain stiffness is controlled by a single parameter, the persistence length, which may be matched to the material of interest. Comparisons of the predicted intermolecular radial distribution functions to the molecular dynamics results of Grest and Kremer for chains of 50, 100, and 150 sites show very good agreement on all length scales. Parametric studies as a function of chain length and chain stiffness reveal that as the characteristic stiffness is increased beyond three bond lengths, the radial distribution function and isothermal compressibility saturate, becoming relatively insensitive to chain length or stiffness. At low densities the local structure is dominated by a correlation hole, indicating a relative absence of intermolecular neighbors, while at high densities the pair correlation function shows a peak and valley structure, qualitatively similar to that of monatomic fluids. © 1990, American Chemical Society. All rights reserved.