MOLECULAR CURVATURE FRICTION IN MACROMOLECULAR DENSE SYSTEMS

A new concept, named ''molecular curvature friction'', is presented as a tool to describe the collective dynamic interaction of a dense visc oelastic medium (polymer melt or network) with a reference flexible li near chain. The reptation-in-a-tube model is used as a platform to int roduce the new effect. The corrected molecular friction coefficient an d the longest relaxation time increase exponentially with the chain le ngth. In the short-to-intermediate range of lengths of entangled chain s (which seems to comprise the longest tested chains reported in the l iterature) the interplay of the new contribution with chain end effect s (exemplified here by the contour length fluctuation), gives an appar ent power law scaling of the longest relaxation time as a 3.3 to 3.6 p ower 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 expression s.