Viscoelastic properties of entangled flexible polymers

Abstract

Viscoelasticity in polymeric liquids is a natural consequence of macromolecular structure. The distribution of configurations is readily displaced from equilibrium, and the configurations relax much more slowly than in monomeric liquids. As a result, recoil effects and other types of elastic-like behaviour are easily observed, and the stress depends in general on the history of deformation rather than simply the current or rate of strain. These properties are related systematically to molecular size and structure and to the concentration. The experimental laws are now rather well established for concentrated solutions and melts of nearly monodisperse flexible polymers. The chains in this case interpenetrate one another's domains extensively, and their dynamics in that tangled environment appear to depend in a universal way on mutual ‘uncrossability’. The proposal that linear chains in this circumstance move to new conformations primarily by diffusion along their own lengths has recently been developed into a full theory of entangled-chain dynamics. Tests of this theory and proposals for its modification to include other motions are discussed.