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