Molecular observation of contour length fluctuations in polymer melts

Abstract

The close comparison of linear rheology data of some long-chain polymer melts with the reptation model indicates the existence of additional degrees of freedom limiting the topological chain confinement. As one candidate contour length fluctuations (CLF) were proposed and indeed account for the observed power law in the dynamic loss modulus G″( ω). In order to study these mechanisms on a microscopic scale we have performed neutron spin echo investigations of the single-chain dynamic structure factor from polyethylene (PE) melts over a large range of chain lengths. A systematic loosening of the confinement with decreasing chain length is found and can be described quantitatively by the effect of CLF on the confining tube establishing this mechanism on a molecular level in space and time.