Spin-echo spectrometer with time-of-flight option and focusing option

Polymer reptation

In the melt, long chain polymers heavily interpenetrate each other and mutually restrict their motions in forming topological constraints. In his famous reptation model, de Gennes described the effect of these entanglements by a tube along the coarse grained chain profile localizing the chain and confining the chain motion.

NSE measurements on IN15 for different molecular weight PE polymers corroborated this reptation model. A systematic loosening of the confinement with decreasing chain length is found. The dynamic-structure factors are quantitatively described by the effect of contour-length fluctuations on the confining tube, establishing this mechanism on a molecular level in space and time.

Ref: A. Wischnewski, M. Monkenbusch, L. Willner, et al., Phys. Rev. Lett. 88, 058301 (2002).