On the spontaneous symmetry breaking in the mesophases of achiral banana-shaped molecules

Nemoptic - 1 rue Guynemer, 78114 Magny-les-Hameaux, France and Institute of Solid State Physics, Bulgarian Academy of Sciences 72 blvd. Tsarigradsko Chaussee, 1784 Sofia, Bulgaria

Received: 19 April 2001
Accepted: 19 July 2001

Abstract

We propose that the natural tendency of banana-shaped mesogen molecules to induce a local bend of the nematic director can result in pathological elasticity, with negative bend elastic constant. Under this hypothesis, a simple Landau-like phenomenological model predicts a symmetry-breaking transition inside the nematic phase, from uniform textures toward spontaneous periodic distortion, either oscillating splay-bend or conical twist-bend helix. The predicted lower symmetry nematic phases are expected to show interesting polar properties, similar to those already reported for banana-shaped smectogens.