RELAXATION IN A CONFINED AND ENTANGLED POLYMER LIQUID

We investigate the dynamics of a monodisperse polymer melt that is con fined to the vicinity of a plane by a harmonic potential. Polymer mole cules are represented by harmonic bead-spring chains with fluctuating bead mobility tensors. Mobility fluctuation rates are determined self- consistently from the chain dynamics. The calculation of the viscoelas tic shear modulus is mapped onto the solution of a dynamically disorde red random walk, in which a walker hops among lattice sites with fluct uating hopping rates. The relevant random walk problems are solved wit hin the effective medium approximation, yielding the shear modulus and coefficient of shear viscosity as functions of chain length, entangle ment molecular weight, and strength of the confining potential. Calcul ations illustrate the competition between entanglement effects, which retard chain dynamics, and the effect of the external field, which pro motes relaxation. (C) 1997 American Institute of Physics.