Local structure of model polymeric fluids: Hard-sphere chains and the three-dimensional fluctuating bond model

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Abstract
Monte Carlo simulations are performed for athermal polymers in the three-dimensional fluctuating bond lattice model. Polymer molecules composed of 20 and 50 freely-jointed beads are studied at volume fractions ranging from 0.2 to 0.35. Chain dimensions, intramolecular correlation functions, and intermolecular correlation functions are compared to results of off-lattice simulations for a similar freely-jointed chain model. It is found that the intramolecular correlation functions are qualitatively similar both on and off the lattice; there are quantitative differences which arise because of the larger persistence lengths of the off-lattice chains. At low densities the intermolecular correlation functions are similar in the two models, but significant differences appear at higher densities because of the limited extent of packing in the lattice fluid. We conclude that the lattice model adequately describes the effect of configurational entropy on fluid structure, but is inadequate to address packing effects which are important in the study of polymer melts. The volumetric behavior of the two model fluids is also discussed.