Molecular “curvature friction” in macromolecular dense systems

Department of Solid State Physics, Risoe National Laboratory, P.O. box 49, DK-4000, Røskilde, Denmark

Received: 25 November 1996
Accepted: 10 July 1997

Abstract

A new concept, named “molecular curvature friction”, is presented as a tool to describe the collective dynamic interaction of a dense viscoelastic medium (polymer melt or network) with a reference flexible linear chain. The reptation-in-a-tube model is used as a platform to introduce the new effect. The corrected molecular friction coefficient and the longest relaxation time increase exponentially with the chain length. In the short-to-intermediate range of lengths of entangled chains (which seems to comprise the longest tested chains reported in the literature) the interplay of the new contribution with chain end effects (exemplified here by the contour length fluctuation), gives an apparent power law scaling of the longest relaxation time as a 3.3 to 3.6 power of the chain length. In the same range the two effects result in an apparent power law scaling of the self-diffusion coefficient as a -2.1 to -2.3 power of the chain length. Three sets of experimental data on longest relaxation time, self-diffusion coefficient and zero shear-rate viscosity were very well fitted by the respective new expressions.