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arXiv 0811.3396cond-mat.softphysics.chem-ph
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polymer玻璃中局域动力学的反常性质

Anomalous properties of the local dynamics in polymer glasses

R. Casalini, C. M. Roland

摘要:

纳米科学的出现增加了能够探测材料的非常局部结构的实验的重要性,特别是对于无序和异质系统。这在技术上很重要;例如,玻璃状聚合物的纳米级结构与它们的宏观物理性质直接相关。我们已经发现了一个局部的,高频动态过程可以用来监测,甚至预测玻璃状聚合物的宏观行为。通过不同的化学和热力学途径玻璃化的聚乙烯在玻璃态下表现出不同的密度。我们发现,一个高频率的弛豫模式(Johari-Goldstein过程涉及的链骨架的片段的局部运动)的速率和振幅可以与密度相关或反相关。这意味着,无论是未被占用的(自由)体积,也没有组态熵控制在任何一般意义上的局部动力学。相反,是局部密度波动的幅度构成了这些纳米尺度运动的基础。我们展示了如何的动力学和密度波动的属性都可以解释在一个不对称的双势阱。最后,由于波动的宏观性质的基础上,我们认为,后者的信息应该是从本地动态的表征。

英文摘要:

The emergence of nanoscience has increased the importance of experiments able to probe the very local structure of materials, especially for disordered and heterogeneous systems. This is technologically important; for example, the nanoscale structure of glassy polymers has a direct correlation with their macroscopic physical properties. We have discovered how a local, high frequency dynamic process can be used to monitor and even predict macroscopic behavior in glassy polymers. Polyvinylethylenes vitrified by different chemical and thermodynamic pathways exhibit different densities in the glassy state. We find that the rate and amplitude of a high frequency relaxation mode (the Johari-Goldstein process involving local motion of segments of the chain backbone) can either correlate or anti-correlate with the density. This implies that neither the unoccupied (free) volume nor the configurational entropy governs the local dynamics in any general sense. Rather it is the magnitude of the fluctuations in local density that underlie these nm-scale motions. We show how properties of the dynamics and the density fluctuations can both be interpreted in terms of an asymmetric double well potential. Finally, since fluctuations underlie the macroscopic properties, we argue that information about the latter should be obtainable from characterization of the local dynamics.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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