Universal law for the rotational viscosity of nematic liquid crystals

The rotational viscosity ${\gamma }_1\mathrm{}\left(T\right)\mathrm{}$ of a nematic is of dominant importance for wide operating temperature display applications. In this paper we show that ${\gamma }_1\mathrm{}\left(T\right)\mathrm{}$ is, except for a small prefactor variation, a universal function of $T-T_g$ where $T_g$ is the glass transition temperature. In a mixture $T_g$ is a linear function of the component mole fractions and $T_g$ of a component can be predicted from molecular structure by a simple phenomenological model. ${\gamma }_1\mathrm{}\left(T\right)\mathrm{}$ of a mixture can thus be predicted from the molecular structures and concentrations of the components.