Integral Equation Theory of Polymer Melts: Density Fluctuations, Static Structure Factor, and Comparison with Incompressible and Continuum Limit Models

A detailed numerical study, utilizing our RISM integral equation theory, of the static structure factor and isothermal compressibility of athermal polymer melts composed of nonoverlapping freely jointed chains is reported. Trends associated with variable density, degree of polymerization, and intramolecular details are established. At small wave vectors a crossover in the behavior of the structure factor from semidilute-like Lorentzian decay to simple liquid behavior is found with increasing (decreasing) melt density (molecular weight). Comparison of the integral equation theory predictions for the intermolecular pair correlation function with those of a simple incompressible model and an analytical continuum limit model is carried out.