Eur. Phys. J. E (2006) 19: 489-500
https://doi.org/10.1140/epje/i2006-10004-6

Regular Article

Zigzag instability of a χ disclination line in a cholesteric liquid crystal

Laboratoire de Physique de l'Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364, Lyon Cedex 07, France

^* e-mail: alain.dequidt@ens-lyon.fr
^** e-mail: patrick.oswald@ens-lyon.fr

Received: 16 January 2006
Accepted: 22 February 2006
Published online: 13 April 2006

Abstract

We studied the formation of χ disclination lines in planar cholesteric samples placed in a temperature gradient near the cholesteric to smectic A phase transition. We observed that the first simple line which forms close to the smectic-cholesteric front zigzags when it is perpendicular to the direction of planar anchoring and is straight for other orientations. This instability is similar to Herring instability for crystalline surfaces. We show numerically that it originates from a strong increase of the elastic anisotropy close to the transition. In addition, we propose a new method to measure the pitch divergence at the smectic to cholesteric phase transition.