NMR Observations of Entangled Polymer Dynamics: Focus on Tagged Chain Rotational Dynamics and Confirmation from a Simulation Model
NMR Observations of Entangled Polymer Dynamics: Focus on Tagged Chain Rotational Dynamics and Confirmation from a Simulation Model
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DOI：
10.1021/ma4021938
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发表时间：
2014-01-14
期刊：
影响因子：
5.5
通讯作者：
Panja, Debabrata
中科院分区：
文献类型：
--
作者：
Furtado, Filipe;Damron, Joshua;Panja, Debabrata
由于缺乏解决相当长的相关时间尺度的方法，对高分子量链的纠缠动力学，特别是管模型的区域II-IV中的较慢链模式的分子水平的洞察仍然很少。在理论方面，在足够大的系统中，新的计算机模拟方法刚刚达到相应的时间尺度。在这里，我们面对最近的多量子质子核磁共振方法的结果与一个新的晶格模型的结果。我们解决了这样的担忧，即质子核磁共振依赖于邻近原子核之间的偶极-偶极耦合，不仅对反映管模型所需细节或可能需要的修改的链内旋转运动是固有的敏感，而且对通过链间偶极-偶极耦合相互传递的链的平移扩散敏感。为了批判性地评估后者的影响，我们在这里介绍了同位素稀释实验的结果，其中数据主要反映了标记链的动力学。我们发现，链间偶极-偶极耦合对所提取的取向自相关函数的形状有微弱的影响，实验数据和计算机模拟数据非常吻合。我们的结论是，核磁共振方法和新的晶格模型真实地反映了纠缠链动力学的普遍特征，特别是在微观水平上与简单的管状模型预测的偏差。
Molecular-level insights into the entangled dynamics of high-molecular-weight chains, in particular of slower chain modes in regimes II-IV of the tube model, are still rare due to the lack of methods resolving the rather long associated time scales. On the theoretical side, new computer simulation methods are just reaching the relevant time scales in sufficiently large systems. Here, we confront results from a recent multiple-quantum proton NMR method with results from a novel lattice model. We address the concern that proton NMR, relying on the dipole-dipole couplings between nearby nuclei, is intrinsically sensitive not only to intrachain rotational motions which reflect the desired details of the tube model or possibly necessary modifications, but also to the translational diffusion of chains past each other via interchain dipole-dipole couplings. In order to critically assess the influence of the latter, we here present results of isotope-dilution experiments, in which the data reflect mainly tagged-chain dynamics. We find overall weak effects of interchain dipole-dipole couplings on the shape of the extracted orientation autocorrelation function and very good agreement of the experimental and the computer simulation data. We conclude that the NMR method as well as the novel lattice model faithfully reflects the universal features of entangled chain dynamics and in particular the deviations from simple tube-model predictions on a microscopic level.