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NMR Rescaling Revisited

机译：NMR重新定标

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摘要

The purpose of this work is to examine the approximation known as NMR rescaling, in which a polymer chain is replaced by a series of NMR submolecules. This coarse graining of the atomistic details makes various NMR calculations analytically possible. To test the accuracy of this approach a computer simulation of network chains consisting of freely jointed rigid rods has been carried out. The time dependence of the orientation of these rods relative to their network chain end-to-end vector has been recorded. From this the NMR Hahn spin echo sampled transverse relaxation and double quantum build-up and subsequent decay have been calculated. The simulated NMR signals are then compared with theoretical results derived from a rescaling approach. In this work we also test the Anderson-Weiss second moment approximation by using it to derive analytical expressions for the NMR signals for the simulated chains, which can then be directly compared with the simulated results. From this work it is shown that for a polymer melt above its glass transition temperature both rescaling and the second moment approximations are valid.
机译：这项工作的目的是研究称为NMR重缩放的近似方法，其中聚合物链被一系列NMR亚分子取代。原子细节的这种粗粒度使得分析各种NMR计算成为可能。为了测试这种方法的准确性，对由自由连接的刚性杆组成的网络链进行了计算机仿真。这些棒的方向相对于它们的网络链端到端向量的时间依赖性已经被记录下来。据此，已计算出NMR Hahn自旋回波采样的横向弛豫和双量子积累以及随后的衰减。然后将模拟的NMR信号与从重新缩放方法得出的理论结果进行比较。在这项工作中，我们还通过使用它来推导模拟链的NMR信号的解析表达式来测试Anderson-Weiss第二矩近似，然后可以将其与模拟结果直接进行比较。从这项工作表明，对于高于其玻璃化转变温度的聚合物熔体，重新定标和第二矩近似都是有效的。

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