Ry. Dong, DYNAMICS OF A SMECTIC LIQUID-CRYSTAL - DIRECTOR FLUCTUATIONS AND REORIENTATION OF BIAXIAL MOLECULES, Journal of physical chemistry, 100(39), 1996, pp. 15663-15669
We report on the measurements of quadrupolar splittings and spectral d
ensities in the mesophases of a partially deuterated smectogen -butoxy
benzylidene-4'-n-octylaniline-2,3,5,6,-d(4) at two different Larmor fr
equencies. A broad-band multiple-pulse sequence was used to simultaneo
usly measure the Zeeman and quadrupolar spin-lattice relaxation times.
Using a model that combines molecular rotational diffusion of an asym
metric rotor and order director fluctuations, the measured spectral de
nsities for the ring and C-alpha deuterons in the nematic and smectic
A phases were accounted quantitatively. The contributions from directo
r fluctuations were taken to second order for both J(1)(omega) and J(2
)(2 omega). A global target approach was used to derive the motional p
arameters and a molecular prefactor for director fluctuations. It was
found that the activation energy for spinning motions is lower than th
at for tumbling motions of the liquid crystal molecule.