J. Phys. II France
Volume 1, Numéro 12, December 1991
Page(s) 1455 - 1464
DOI: 10.1051/jp2:1991162
J. Phys. II France 1 (1991) 1455-1464

Hydrodynamic and electrohydrodynamic properties of the smectic ${\rm C_M}$ phase in liquid crystals

Helmut R. Brand and Harald Pleiner

FB 7, Physik, Universität Essen, D 4300 Essen 1, Germany

(Received 3 June 1991, revised 22 July 1991, accepted 16 September 1991)

We present the hydrodynamic and electrohydrodynamic equations for the liquid crystalline smectic ${\rm C_M}$ phase. This phase, which is fluid in the layers, orthogonal and optically biaxial, has recently been found experimentally in polymeric liquid crystals. We compare the macroscopic properties of the ${\rm C_M}$ phase with those of the classical fluid smectic phases, namely smectic A, which is uniaxial, and the classical smectic C phase, that is tilted and biaxial. We predict that the in-plane director in the ${\rm C_M}$ phase can show flow alignment. We point out that the chiralized version of smectic ${\rm C_M}$, ${\rm C^*_M}$, has electromechanical properties, that are qualitatively different from those of chiral smectic ${\rm C^*}$, but rather similar to those of a classical cholosteric phase. In contrast to ${\rm C^*}$, ${\rm C^*_M}$ is not helielectric and thus does not show a linear response to an externally applied spatially homogeneous electric field, except for an electroclinic effect near phase transitions to a tilted phase. But similarly to ${\rm C^*}$ and cholesterics it is predicted to show piezoelectricity.

© Les Editions de Physique 1991