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

该项目的目的是利用1H和19F自旋晶格弛豫来研究粘性液体的平动和转动动力学。这种弛豫包括两个贡献：第一个是由与转动动力学有关的分子内偶极-偶极相互作用的涨落引起的，第二个是主要由平移运动(扩散)介导的分子间涨落引起的。应用覆盖10 kHz-20 MHz(1H)频率范围的现代FC核磁共振，我们的准备工作表明，分子间和分子内弛豫谱可以明确地分开，而不需要繁琐的同位素稀释。因此，核磁共振弛豫计量学为通过一次实验研究平动和转动动力学提供了一个独特的机会。弛豫谱的形状提供了有关运动机制的信息，通过应用适当的分子间贡献模型，可以在较宽的温度范围内提取扩散系数。这将被用于具有逐渐增加的关于动力学和自旋属性的复杂性的液体。此外，还将进行分子动力学模拟，以提供广泛适用的分子间光谱描述。提取的旋转贡献将与2H核磁共振和介电光谱的结果进行比较，这两个结果都是探测分子旋转。对于平移扩散，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.