BROWNIAN DYNAMICS OF NONDILUTE SOLUTIONS OF RODLIKE POLYMERS .2. HIGH-CONCENTRATIONS

We report the results of Brownian dynamics simulations for solutions of rigid rodlike polymers with an aspect ratio of 50 at high concentrations (70–150 rods/L3, where L is the molecular length). Many-body contributions to the static properties were found to be much weaker than direct two-body interactions up to the highest concentration simulated; therefore the local structure was mostly determined by independent binary interactions. Furthermore, the solvent–polymer impacts in between rod-rod collisions killed most of the temporal correlation of successive rod-rod collisions reducing in this way a highly correlated rod–rod collision sequence to a series of almostuncorrelated binary collisions. At sufficiently high concentrations (higher than 90 rods/L3) the translational diffusivity normal to the rod axis froze, which proves the existence of completely closed cages. In this concentration regime our simulation results for the rotational diffusivity fall between the predictions of the Doi–Edwards theory for rods with finite diameter and those of Fixman’s model. The discrepancy between Fixman’s model and our simulation results at high concentrations probably originates from the very sharp decrease of the equilibrium cage size with concentration, which could make the short time relaxation mechanism introduced by Fixman inefficient. © 1990, American Chemical Society. All rights reserved.