Low frequency NMR relaxometry for the study of polymer dynamics

我们计划结合场循环(FC)和场梯度(FG)-核磁共振来研究线性聚合物熔体的集体动力学。将系统地使用第一个资助期的工具性成果。例如，与频率相关的弛豫速率现在覆盖从40 MHz到大约300赫兹的范围。对于其他聚合物体系，应进一步研究管状爬行模型的不足之处，并将考虑聚合物动力学的替代模型。此外，还将分析我们的FC数据、双量子核磁共振数据(K.Saalwächter，Halle)和通用模拟之间的差异。总体目标是找出管状翻转模型在多大程度上将其有效性保持在微观水平上。我们计划通过在2H弛豫色散处系统地寻找第一个来开始测量纯重新取向动力学。这些实验将补充从1H/2H稀释实验中提取的链内1H驰豫速率弥散和链间速率弥散的测定。两者的相对贡献提供了关于微观动力学的有价值的信息，并允许区分不同的聚合物模型。我们将从中间速率推导出均方位移(MSD)，并将这些结果与直接测量的FG数据相结合。通过这种方式，我们第一次能够在MSD方面覆盖整个次扩散制度。在理论部分，我们邀请了N.Fatkullin教授(喀山)作为同事。同时，仪器的发展也将得到进一步的推进。我们将尝试将1H频率降至远低于100赫兹的常规频率，这比商业机器的频率低两个数量级以上。有了如此宽的频率范围，我们可以真正地认为FC弛豫法是研究各种软物质系统的一种强大的分子流变学方法。

We plan to combine field-cycling (FC)- and field-gradient (FG)-NMR for studying the collective dynamics of linear polymer melts. The instrumental achievements of the first funding period will be used in a systematic way. For instance, the frequency dependent relaxation rate now covers a range from 40 MHz down to about 300Hz. Hints for deficiencies of the tube-reptation model shall be further examined for other polymer systems, and alternative models for the polymer dynamics will be considered. Further, discrepancies between our FC data, double quantum NMR data (K. Saalwächter, Halle) and generic simulations will be analyzed. The overall goal is to find out to which extent the tube-reptation model keeps its validity at a microscopic level. We plan to start measurements of the pure reorientation dynamics by looking for the first systematically at the 2H relaxation dispersion. These experiments will complement the determination of the intrachain 1H relaxation rate dispersion and the interchain rate dispersion, extracted from 1H/2H dilution experiments. The relative contribution of both provides valuable information on the microscopic dynamics and allows discriminating different polymer models. From the inter rate we will deduce the mean squared displacement (MSD) and combine these results with directly measured FG data. In this way we are able, for the first time, to cover the whole sub-diffusive regime in terms of the MSD. For the theory part we have gained Prof. N. Fatkullin (Kazan) as a coworker. Also, the instrumental development will be further pushed forward. We will try to reach down to 1H frequencies well below 100 Hz routinely, which is more than two orders of magnitude below those of commercial machines. With such a wide frequency span we can truly consider FC relaxometry as a powerful molecular rheology method for studying diverse soft matter systems.