NMR study of diffusive processes in novel liquid crystalline phases

Various deuterium one- and two-dimensional (2D) NMR techniques are used in the present study to characterize molecular self-diffusive processes in some novel mesophases. Both aligned and powder samples of liquid crystals (LC) are chosen to investigate rotational and/or translational jump diffusions. It is demonstrated that rotation of aligned LC samples in a NMR goniometer probe can be helpful in obtaining dynamic and structural information. Both spectral simulations and/or pulse separation (τ) dependences of the quadrupole echo intensity are successfully employed. Deuteron spin-lattice relaxation times and angle dependent spectra are measured in a columnar phase of a monomeric discotogen to illustrate both the fast and intermediate motion regimes. Jump diffusions of chiral rodlike molecules in various smectic C⁎ (SmC⁎) phases and twist grain boundary A⁎ (TGBA⁎) phase are studied. In the LC 10B1M7, the jump rate (or diffusion constant) is determined as a function of temperature in the ferro-, ferri- and antiferro-electric chiral C⁎ phases. 2D deuterium exchange NMR is used to monitor the dynamic processes (self-diffusion) in the ferroelectric SmC⁎ and TGBA⁎ phases. Moreover, packing information of the phase can also be obtained in the two ferrielectric subphases and TGBA⁎ phase, which can be compared with results obtained by X-rays measurements.