Orientational order parameter and rotational viscosity in C60 doped E7 nematic liquid crystal

The reorientational order parameter dependent complex linear susceptibilities are derived based on the angular averaged linear response theory of the molecular polarizability, which includes the Vuks type equations of anisotropic refractive indices and absorbances. The polar angular absorbance at 633 nm wavelength is measured as a function of the concentration of fullerene C60 in E7 nematic liquid crystals (NLCs), from which the order parameter is deduced. It is shown that the order parameter has a linear dependence of dopant concentration. We also present a simple optical transmission method by adopting the closed-aperture Z-scan geometry under the influence of switching on and off the dc electric field to determine the optical relaxation time and the rotational viscosity coefficient of C60 doped E7 NLC. The experimental results are pretty well explained by using the Osipov–Terentjev theory of the rotational viscosity with the measured order parameter.