A nonreptation model for polymer dynamics in the melt and concentrated solutions

A model for the motion of a dense multichain polymer system involving linear chains is presented. The model is based on the assumption that chain motion perpendicular to the direction of the chain backbone dominates the dynamics over motion along the backbone. This model is motivated by the results of recent Monte Carlo computer simulations on multichain systems for chain lengths ranging up to 800 segments. It is found in these simulations that motion perpendicular to the backbone dominates. Since many chains are highly intertwined with any given chain, we assume that the chain motion at an interchain contact point proceeds by sliding along the contour of each entangling chain until the exterior of the ball of density formed by the entangling chain is reached. At this point the contact is broken. This requirement that a chain move by sliding along the random flight contour of another chain at a contact point results in an effective bead friction coefficient for three-dimensional motion which is an increasing function of time. A continuous distribution of contact times is calculated within this model. The chain dynamics are evaluated within a Rouse-like model employing a time-dependent bead friction coefficient and a time-dependent number of chain segments. The number of segments in the model Rouse chain at time t is equated with the number of contacts of duration longer than t. The asymptotic large N dependencies of the center-of-mass diffusion coefficient and the terminal relaxation time are found to be N−2 and N3, respectively. Calculations are performed for chains of various lengths, and the results of the model are qualitatively very similar to those reported from the Monte Carlo simulations.