Nematiclike viscosity coefficients of ferroelectric liquid crystals in their smectic-C^* phase

The five nematiclike viscosity coefficients corresponding to the Smectic-C^* (SmC^*) phase are calculated by a combination of the existing statistical-mechanical approach and NMR theory, based on a rotational diffusion model for two ferroelectric smectogens. The order parameter S₂, the smectic tilt angle , and the rotational diffusion coefficient D, corresponding to molecular tumbling in the SmC^* phase, for the ferroelectric smectogens 4-[4-(1-methylheptyloxy)]biphenyl-(10-undecenyloxy)benzoate and (S)-[4-(2-methylbutyl)phenyl]-4-n-octylbiphenylcarboxylate have been obtained by means of ²H NMR spectroscopy and these data have been used to calculate viscosity quantities. For practical purposes a specific form of the functional dependence of S₄ on S₂ is used. As the main result, our calculations also predict a laminar flow regime in a high shear flow for these liquid crystal compounds.

©2006 The American Physical Society