The effects of bead-bead repulsion on the spacial and time correlation functions of model polymer solutions: Mesoscale simulations

Brownian dynamics simulations have been carried out for model polymer chain s in a good solvent over a wide concentration range. The polymers were trea ted as beads linked by finitely extensible nonlinear elastic (FENE) springs and the repulsion between any two unlinked beads was modeled by a pair pot ential with a Gaussian analytic form, beta u(r) = A exp(-r(2)/sigma(2)), wh ere beta = 1/kT, A and sigma are characteristic energy and distance scales, respectively. The effects of the bead-bead repulsion on the structure and time-correlation functions of the chains in the polymer solution were studi ed as a function of polymer concentration. Three concentration regimes are distinguished, a dilute region where intrachain bead-bead repulsions domina te, a concentrated region where interchain bead-bead repulsions dominate, a nd a highly concentrated region where the net repulsion on any bead tends t o zero owing to substantial cancellation of the effects from nearest neighb ors. The pair radial distribution function, the relaxation time for the rot ation of the coil, the mean square displacement of the middle-bead and that of the center of mass of the chain, the infinity frequency elastic modulus , and the viscosity of the system are examined in all the density regions. Our results show that the excluded volume repulsion strongly affects the be havior of the system in the concentrated region and that the structural fea tures return to the Rouse-limit behavior at high density more rapidly than the dynamical properties. (C) 1999 American Institute of Physics. [S0021-96 06(99)51247-6].