Direct Measurement of Molecular Mobility in Actively Deformed Polymer Glasses
Direct Measurement of Molecular Mobility in Actively Deformed Polymer Glasses
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DOI：
10.1126/science.1165995
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发表时间：
2009-01-09
期刊：
影响因子：
56.9
通讯作者：
Ediger, M. D.
中科院分区：
文献类型：
--
作者：
Lee, Hau-Nan;Paeng, Keewook;Ediger, M. D.
当足够的力作用于玻璃聚合物时，它开始通过聚合物链的运动而变形。我们使用光学光漂白技术来定量测量聚合物玻璃[聚甲基丙烯酸甲酯]在主动变形过程中分子迁移率的变化。在单轴拉伸蠕变过程中，节段的流动性增加了1000倍。虽然Eyring模型可以描述低应力下的迁移率增加，但它不能描述流动开始后的迁移率。在这种情况下，流动性大大加快，松弛时间的分布大大收窄，表明局部环境的整体更加均匀。在更大的应力下，在应变硬化区域，迁移率随着应力的增加而降低。与应力诱导的流动性允许塑料在聚合物玻璃中流动的观点一致，我们观察到蠕变过程中应变速率和节段流动性之间存在很强的相关性。
When sufficient force is applied to a glassy polymer, it begins to deform through movement of the polymer chains. We used an optical photobleaching technique to quantitatively measure changes in molecular mobility during the active deformation of a polymer glass [ poly( methyl methacrylate)]. Segmental mobility increases by up to a factor of 1000 during uniaxial tensile creep. Although the Eyring model can describe the increase in mobility at low stress, it fails to describe mobility after flow onset. In this regime, mobility is strongly accelerated and the distribution of relaxation times narrows substantially, indicating a more homogeneous ensemble of local environments. At even larger stresses, in the strain- hardening regime, mobility decreases with increasing stress. Consistent with the view that stress- induced mobility allows plastic flow in polymer glasses, we observed a strong correlation between strain rate and segmental mobility during creep.