Molecular dynamics study of the ferroelectric liquid crystal CI IPNOC by proton spin-lattice relaxation

Abstract

Proton spin-lattice relaxation studies were carried out in the S, and S z phases of the liquid crystal C1 IPNOC using both conventional and fast field cycling NMR techniques. Ti dispersion curves were obtained at two different temperatures for each mesophase covering frequencies from lo2 to 3 x 10' Hz. In both mesophases the TI 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, 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 S, and the S z phases.

Molecular Dynamics in the Columnar and Lamellar Mesophases of a Liquid Crystal of Biforked Molecules

“…The a>~1 dependence resulting from the layer undulation mechanism is in good agreement with our data in this phase. Similar values for the observed low and high cut-off frequencies can be found in the literature for disordered layer smectic phases in other liquid crystalline materials [30]. (£J / 2n)/Hz…”

“…Our calculations are independent of the tilt angle of the phase, <p, because this parameter is averaged out in the case of a powder sample as we can easily verify applying (3), (4) and 7with A = (p. The values of r± obtained from the fits for the three measured temperatures in the S c phase are of the order of 10" 9 s and are compatible with a thermally activated process with an activation energy of 42 kJ mol -1 . The values of tx and D _ obtained for the S c phase and the respective activation energy, presented in Table 1, are similar to values for the same phase reported in [29][30]. The value of d (that may be assigned to the spacing corresponding to the lateral intermolecular interaction between the molecular hard cores) is in good agreement with the structural results presented in [6].…”

Nuclear magnetic resonance studies of translational diffusion in thermotropic ionic liquid crystals

“…The diffusion coefficients in the mesophases were also obtained from the T 1 relaxation time measurements [33][34][35]. Estimation of the diffusion coefficients from Figure 2.…”

Molecular dynamics in a blue phase liquid crystal: a 1H fast field-cycling NMR relaxometry study

“…This description of T 1 À1 was also found for SmC* phases of other liquid crystals. 34,44 The contribution of in-plane tilt direction uctuations (T 1…”