Translational and rotational motion in liquids by means of field cycling NMR

该项目的目的是通过应用场循环（FC）核磁共振揭示的1H和19F自旋晶格弛豫来研究粘性液体的平移和旋转动力学。弛豫包括两个贡献：第一个是由分子内与旋转动力学有关的偶极-偶极相互作用的波动引起的，第二个是由主要由平移运动（扩散）介导的分子间波动引起的。应用现代FC核磁共振，覆盖频率范围为10 kHz - 20 MHz (1H)，我们的准备工作表明，分子间和分子内的弛豫谱可以明确分离，而不需要繁琐的同位素稀释。因此，核磁共振弛豫测量提供了一个独特的机会，研究平移和旋转动力学通过一个单一的实验。弛豫谱的形状提供了有关运动机理的信息，并且通过应用适当的分子间贡献模型可以在很宽的温度范围内提取扩散系数。这将被用于涉及动力学和自旋性质的复杂性逐渐增加的液体。此外，MD模拟将进行提供分子间光谱的广泛适用的描述。提取的旋转贡献将与2H NMR和介电光谱的结果进行比较，两者都探测分子的旋转。就平移扩散而言，我们的目标是建立核磁共振弛豫法作为梯度核磁共振的补充方法。

The aim of the project is to investigate translational and rotational dynamics of viscous liquids by means of 1H and 19F spin-lattice relaxation revealed by applying field-cycling (FC) NMR. The relaxation includes two contributions: The first one is caused by fluctuations of the intramolecular dipole-dipole interactions which are associated with rotational dynamics, while the second one originates from intermolecular fluctuations mediated mainly by translational motion (diffusion). Applying modern FC NMR, which covers a frequency range of 10 kHz – 20 MHz (1H), our preparatory work shows that the inter- and intramolecular relaxation spectrum can be unambiguously separated, without a need of tedious isotope dilution. Thus, NMR relaxometry gives a unique opportunity to study translational and rotational dynamics by a single experiment. The shape of the relaxation spectra provides information about the motional mechanism, and by applying an appropriate model for the intermolecular contribution the diffusion coefficient can be extracted in a broad temperature range. This will be exploited for liquids with progressively increasing complexity concerning dynamics as well as spin properties. In addition, MD simulations will be carried out to provide a broadly applicable description of the intermolecular spectrum. The extracted rotational contribution will be compared with results from 2H NMR and dielectric spectroscopy, both probing molecular rotations. As far as the translational diffusion is concerned, we aim at establishing NMR relaxometry as a complementary method to gradient NMR.