Ferroelectric-ferroelastic phase transition in a nematic liquid crystal

TL;DR

This paper demonstrates that ferroelectric ordering in nematic liquid crystals induces a splay phase transition characterized by dielectric and optical evidence, supported by theoretical modeling.

Contribution

It provides experimental evidence linking ferroelectric ordering to splay nematic phases and offers a theoretical framework for understanding this transition.

Findings

Ferroelectric ordering causes splay nematic phase formation.

The phase transition exhibits ferroelectric characteristics confirmed by dielectric spectroscopy.

Splay modulation period is approximately 5-10 microns, confirmed by SHG and microscopy.

Abstract

Ferroelectric ordering in liquids is a fundamental question of physics. Here, we show that ferroelectric ordering of the molecules causes formation of recently reported splay nematic liquid-crystalline phase. As shown by dielectric spectroscopy, the transition between the uniaxial and the splay nematic phase has the characteristics of a ferroelectric phase transition, which drives an orientational ferroelastic transition via flexoelectric coupling. The polarity of the splay phase was proven by second harmonic generation (SHG) imaging, which additionally allowed for determination of the splay modulation period to be of the order of 5 - 10 microns, also confirmed by polarized optical microscopy. The observations can be quantitatively described by a Landau-de Gennes type of macroscopic theory.