Rotational viscosity of nematic liquid crystals A critical examination of existing models

A simple electro-optical method was developed to characterize the temperature dependent viscoelastic coefficient of six nematic liquid crystals with different conjugation lengths. Results were then used to test seven most frequently used models for rotational viscosity (y1). Computer results show that some models fit certain specific liquid crystals but, in general, two models fit all the experimental data. These two models are y 1 = α2 S 2 exp[E/k(T - T 0)] and y 1 = (α1 S + α2 S 2) exp (E/kT), with α1, α2 E, and T 0 as adjustable parameters.