Investigations of static properties of model bulk polymer fluids

The static properties of continuum, multichain systems are investigated by a "reptation" Monte Carlo algorithm. All beads interact via a repulsive (shifted) Lennard-Jones potential. In addition, nearest neighbors along chains are linked by a quasiharmonic potential which permits limited pair extensions. Chain lengths of 5, 10, 20, 32, 50, and 70 beads have been studied. Studies at densities of 0.1, 0.3, and 0.5 demonstrate that chain dimensions are compressed as the concentration is increased. Both the mean square end-to-end distance, 〈R²〉, and the mean square radius of gyration, 〈S²〉, have a power law dependence upon l-1, the number of bonds, with exponent approximately 1.16 for ρ=0.1 and 1.07 for ρ=0.3 and 0.5. 〈R²〉 and 〈S²〉 scale with density as ρ^-γ where γ∼-0.22±0.02 for long chains, in reasonable agreement with the scaling prediction of -0.25. The asphericity ratios, the pair correlation functions of the center of masses, and the extent of chain overlaps indicate the nonideal behavior of these systems.