Zamponi M, Wischnewski A, Monkenbusch M, Willner L, Richter D, Falus P, Farago B, Guenza M G
Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, Germany.
J Phys Chem B. 2008 Dec 18;112(50):16220-9. doi: 10.1021/jp807035z.
We present a comparison between theoretical predictions of the generalized Langevin equation for cooperative dynamics (CDGLE) and neutron spin echo data of dynamic structure factors for polyethylene melts. Experiments cover an extended range of length and time scales, providing a compelling test for the theoretical approach. Samples investigated include chains with increasing molecular weights undergoing dynamics across the unentangled to entangled transition. Measured center-of-mass (com) mean-square displacements display a crossover from subdiffusive to diffusive dynamics. The generalized Langevin equation for cooperative dynamics relates this anomalous diffusion to the presence of the interpolymer potential, which correlates the dynamics of a group of slowly diffusing molecules in a dynamically heterogeneous liquid. Theoretical predictions of the subdiffusive behavior, of its crossover to free diffusion, and of the number of macromolecules undergoing cooperative motion are in quantitative agreement with experiments.
我们展示了用于协同动力学的广义朗之万方程（CDGLE）的理论预测与聚乙烯熔体动态结构因子的中子自旋回波数据之间的比较。实验涵盖了广泛的长度和时间尺度范围，为该理论方法提供了有力的检验。所研究的样品包括分子量不断增加的链，其动力学过程跨越了从非缠结到缠结的转变。测量得到的质心（com）均方位移显示出从亚扩散动力学到扩散动力学的转变。用于协同动力学的广义朗之万方程将这种反常扩散与聚合物间势的存在联系起来，该势使动态非均匀液体中一组缓慢扩散分子的动力学相互关联。亚扩散行为、其向自由扩散的转变以及参与协同运动的大分子数量的理论预测与实验结果在定量上是一致的。
