Banana and pizza-slice-shaped mesogens give a new constrained ferromagnet universality class

TL;DR

This paper introduces a new universality class for phase transitions in liquid crystals composed of banana and pizza-slice-shaped molecules, revealing novel phases when splay and bend elastic constants are negative.

Contribution

It extends theoretical models to include negative splay and bend elastic constants for polar molecules, discovering new phases and a novel universality class.

Findings

Discovered two new liquid crystalline phases with negative elastic constants.

Identified a new constrained ferromagnet universality class for phase transitions.

Extended Frank elastic energy models to polar banana and pizza-slice-shaped molecules.

Abstract

It has been known that at high density, the local orientation of banana-shaped molecules shows a spontaneously bent state, giving rise to interesting liquid-crystalline phases such as splay-bend and twist-bend. This spontaneous bend can be modelled theoretically by allowing the bend elastic constant in the Frank elastic energy to become negative. Here we extend this idea to polar banana and pizza-slice-shaped molecules which can also splay spontaneously. By allowing both splay and bend elastic constants to be negative we discovered two additional new liquid crystalline phases. In particular, using renormalization group technique, we showed that the phase transition belongs to a new constrained ferromagnet universality class.