Dynamics of Freedericksz Deformation near a Nematic—Smectic-ATransition

We have used the dynamic Freedericksz-deformation method to measure in detail the temperature dependence of the twist viscosity ${\gamma }_1$ in N-$p$-cyanobenzylidene-$p$-octyloxyaniline near the nematic-smectic-$A$ transition. We have demonstrated that the intrinsic contribution ${{\gamma }_1}^0$ can be determined independently by extrapolating data on doped samples. Our analysis shows ${\gamma }_1$ to diverge with a critical exponent $\zeta =0.37\mathrm{}\pm 0.05$, in agreement with theoretical expectations.