Theory of acoustic properties near the cholesteric–twisted-grain-boundary-Aphase transition in liquid crystals

Abstract

A theory of sound propagation and attenuation near the cholesteric -twisted-grain-boundary-A phase transition in liquid crystals is presented. A mode-coupling formalism is used to investigate the behavior of the viscosities at the transition. Pretransitional eff'ects are predicted in both the speed of sound and ultrasonic attenuation. The speed of sound is found to exhibit an isotropic dip, and the attenuation coefficient is anisotropic only in the prefactors, having isotropic critical exponents. These results are in qualitative agreement with experiment.PACS number(s): 64.70.Md, 64.60.Ht