Low frequency NMR relaxometry for the study of polymer dynamics

我们计划结合场循环(FC)- nmr和场梯度(FG)- nmr来研究线性聚合物熔体的集体动力学。第一个筹资期的工具性成就将有系统地加以利用。例如，频率相关的松弛率现在涵盖了从40兆赫到大约300赫兹的范围。对于其他聚合物体系，管-复制模型的不足之处有待进一步研究，并将考虑聚合物动力学的替代模型。此外，我们的FC数据，双量子核磁共振数据（K. Saalwächter, Halle）和一般模拟之间的差异将进行分析。总体目标是找出管-复制模型在微观层面上保持其有效性的程度。我们计划通过在2H弛豫色散中寻找第一个系统的重定向动力学来开始纯重定向动力学的测量。这些实验将补充从1H/2H稀释实验中提取的链内1H弛豫速率弥散和链间速率弥散的测定。两者的相对贡献为微观动力学提供了有价值的信息，并允许区分不同的聚合物模型。从中间率我们将推断出均方位移（MSD），并将这些结果与直接测量的FG数据结合起来。通过这种方式，我们第一次能够，用MSD来覆盖整个次扩散状态。在理论部分，我们获得了N. Fatkullin教授（喀山）作为同事。同时，器质性的发展也将进一步向前推进。我们将尝试常规达到远低于100赫兹的1H频率，这比商用机器的频率低两个数量级。有了如此宽的频率跨度，我们可以真正认为FC弛豫法是研究各种软物质系统的强有力的分子流变学方法。

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.