Av. Zakharov et al., Rotational viscosity in a nematic liquid crystal: A theoretical treatment and molecular dynamics simulation, PHYS REV E, 59(6), 1999, pp. 6802-6807
The rotational viscosity coefficient gamma(1) of 4-n-pentyl-4'-cyanobipheny
l in the nematic phase is investigated by combination of existing statistic
al-mechanical approaches (SMAs), based on a rotational diffusion model and
computer simulation technique. The SMAs rest on a model in which it is assu
med that the reorientation of an individual molecule is a stochastic Browni
an motion in a certain potential of mean torque. According to the SMAs, gam
ma(1) is found to be a function of temperature, density, rotational diffusi
on coefficient, and a number of order parameters (OPs). The diffusion coeff
icient and the OPs Hen obtained from an analysis of a trajectory generated
in a molecular dynamics simulation using realistic atom-atom interactions.
In addition, a set of experimentally determined diffusion coefficients and
OPs was used for evaluation of gamma(1). Reasonable agreement between calcu
lated and experimental values of gamma(1) is obtained. It is shown that nea
r the clearing point gamma(1) is proportional to (P) over bar(2)(2) where (
P) over bar(2) is the second-rank OP. This limiting value of gamma(1) is in
agreement with mean-field theory.