Arbe A, Colmenero J
Centro de Física de Materiales (CSIC-UPV/EHU)-Materials Physics Center, Apartado 1072, 20080 San Sebastián, Spain.
Phys Rev E Stat Nonlin Soft Matter Phys. 2009 Oct;80(4 Pt 1):041805. doi: 10.1103/PhysRevE.80.041805. Epub 2009 Oct 14.
By means of time-of-flight neutron scattering, we have characterized the dynamic structure factor and the hydrogen motions of polyethylene above its melting point. As signatures of simple-liquid dynamics, we observe that (i) in the explored dynamic window, the intermediate scattering functions display a single-step decay, without reminiscence of cage effects, and (ii) the structural relaxation as observed at the intermolecular structure factor peak shows a weak temperature dependence, indicating a low degree of interchain cooperativity. However, stretched functional forms are observed for all length scales and temperatures investigated. An apparent direct crossover from the microscopic regime to Rouse-like dynamics suggests an essential role of connectivity in the observed stretching. Finally, while at momentum-transfer values above the structure factor peak the relation between coherent and incoherent characteristic times is reasonably described by the de Gennes narrowing, at larger length scales it is not reproduced by any existing approach.
通过飞行时间中子散射，我们表征了聚乙烯在熔点以上的动态结构因子和氢运动。作为简单液体动力学的特征，我们观察到：（i）在探索的动态窗口中，中间散射函数呈现单步衰减，不存在笼效应的痕迹；（ii）在分子间结构因子峰值处观察到的结构弛豫表现出较弱的温度依赖性，表明链间协同性程度较低。然而，在所研究的所有长度尺度和温度下都观察到了拉伸函数形式。从微观区域到类Rouse动力学的明显直接转变表明连通性在观察到的拉伸中起着重要作用。最后，虽然在结构因子峰值以上的动量转移值处，相干和非相干特征时间之间的关系可以通过德热纳窄化合理描述，但在更大的长度尺度上，任何现有方法都无法重现这种关系。
