Abstract
Proton spin-lattice relaxation studies were carried out in the SA and S*C phases of the liquid crystal CI IPNOC using both conventional and fast field cycling NMR techniques. T 1 dispersion curves were obtained at two different temperatures for each mesophase covering frequencies from 102 to 3 × 108 Hz. In both mesophases the T 1 data can be described assuming the presence of three different relaxation mechanisms, namely local molecular rotations, molecular self-diffusion and collective motions. The self-diffusion constant D 1 was evaluated for several temperatures and the activation energy associated with the diffusion process was obtained. The expected contribution of the soft-mode for the spin-lattice relaxation could not be separated from the contribution of other collective motions. The correlation times associated with the rotations around the molecular long axis and with the fluctuations of this axis were evaluated for both the SA and the S*C phases.