Journal of Chemical Physics vol:118 issue:9 pages:4253-4260
The rotational diffusion coefficient D-perpendicular to, the rotational viscosity coefficients gamma(i) (i=1,2), and the orientational relaxation time tau(00)(1) are investigated. gamma(i) are calculated by a combination of an existing statistical-mechanical approach and of broadband experimental results of the complex permittivity for the polar liquid crystal 4-n-octyl-4'-cyanobiphenyl (8CB). The flow dynamic behavior of the nematic liquid crystal in a shear flow, as well as the transition from a flow alignment regime to a tumbling instability are also investigated in 8CB near and far away of a charged surface. The relaxation of the alignment angle theta(tau) to its equilibrium theta(eq) in a layer up to similar to1.5 mum is calculated using the Ericksen-Leslie theory for the case of planar alignment of 8CB at a charged indium tin oxide-coated glass plate and for the temperature range in which 8CB exhibits a nematic phase. In accordance with earlier Couette flow experiments, our calculations show a tumbling flow in the bulk nematic phase. The nature of the hydrodynamic instability under shear flow, in the vicinity, e.g., at a few tens of mK from a nematic-smectic A phase transition (T-NA) in the nematic phase, and far from T-NA is also discussed for 8CB. (C) 2003 American Institute of Physics.