Entanglements in Polymer Solutions under Elongational Flow: A Combined Study of Chain Stretching, Flow Velocimetry, and Elongational Viscosity

Abstract

The progressive development of entanglements can be detected by observing strain patterns during increasing elongational strain rate where each stage is attributable to a transient network with a lifetime appropriate to the corresponding strain rate. The flow velocities are affected locally bytransient network stretching, and this has pronounced influence on the macroscopic flow resistance(elongational viscosity). The latter should be highly relevant to the interpretation of continuum hydrodynamics of polymer solutions within elongational flow fields in terms of molecular behavior.The present work shows that this will only be possible by taking account of the “microstructure” in molecular strain and in the corr spondingly modified flow velocities, arising as aconsequence of the long relaxation times associated with the stretching of transient networks. © 1988, American Chemical Society. All rights reserved.