J. Physique Lett. 46, 1177-1181 (1985)
DOI: 10.1051/jphyslet:0198500460240117700

AC electric field induced flow and helix unwinding in focal conic texture of smectic C* liquid crystal

B. Labroo, V. Razdan, D.S. Parmar et G. Durand

Department of Physics, University of Kashmir, Srinagar - 190 006, India

Abstract
A thin (˜ 10 μm) focal conic texture of DOBAMBC in its Sm C* phase is submitted to an AC electric field. Above a field threshold, a DC plug flow of the texture normal to the layers is observed. It always originates from the focus of the ellipses towards their centre and extends to the entire focal domain. At higher field, the associated viscous shear unwinds the helical texture. The flow threshold is explained by the build up at the focus of a DC electric pressure, from the action of the AC field on AC space charges, generated by conductivity anisotropy.

Résumé
On soumet une mince (˜ 10 μm) texture à conique focale de DOBAMBC en phase smectique C* à un champ électrique alternatif. Au-delà d'un seuil, un écoulement permanent « bouchon » est observé. Il démarre du foyer des ellipses, vers leur centre. A fort champ, les couples de cisaillement visqueux déroulent la texture hélicoïdale. Le seuil d'écoulement est lié à une pression critique pompée électriquement au coeur des coniques focales, par l'anisotropie de conductivité.

PACS
4765 - Magnetohydrodynamics and electrohydrodynamics.
6130G - Orientational order of liquid crystals in electric and magnetic fields.

Key words
electrohydrodynamics -- organic compounds -- shear flow -- smectic liquid crystals -- space charge -- p decyloxy benzylidene p' amino 2 methyl butyl cinnamate -- AC electric field induced flow -- helix unwinding -- focal conic texture -- smectic C* liquid crystal -- DOBAMBC -- DC plug flow -- associated viscous shear -- DC electric pressure -- AC space charges -- conductivity anisotropy