Perspectives of Deuteron Field-Cycling NMR Relaxometry for Probing Molecular Dynamics in Soft Matter

Due to the single-particle character of the quadrupolar interaction in molecular systems, 2H NMR poses a unique method for probing reorientational dynamics. Spin–lattice relaxation gives access to the spectral density, and its frequency dependency can be monitored by field-cycling (FC) techniques. However, most FC NMR studies employ 1H; the use of 2H is still rare. We report on the application of 2H FC NMR for investigating the dynamics in molecular liquids and polymers. Commercial as well as home-built relaxometers are employed accessing a frequency range from 30 Hz to 6 MHz. Due to low gyromagnetic ratio, high coupling constants, and finite FC switching times, current 2H FC NMR does not reach the dispersion region in liquids (toluene and glycerol), yet good agreement with the results from conventional high-field (HF) relaxation studies is demonstrated. The pronounced difference at low frequencies between 2H and 1H FC NMR data shows the relevance of intermolecular relaxation in the case of 1H NMR. In the...