Determination of the bulk rotational viscosity coefficient in a chiral smectic C* liquid crystal

The method of determination of the bulk values of the rotational viscosity coefficient of the smectic c-director in chiral smectic liquid crystals with a helical structure is described. The measurements were performed using optical detection in the small deformation limit. In contrast to the usual methods, the initial deformation of the helix (caused by strong surface interactions) was avoided by using homeotropic aligned thick samples. The coefficient was measured in 4-methylbutyloxy phenyl-4-octyloxy-benzoate (C8) in the presence of laminar flow. The critical temperature dependence of the measured coefficient was found. The relation between the measured coefficient and the smectic C order parameter is shown.