Splay nematic phase

TL;DR

This paper reports the discovery of a new splay nematic phase in liquid crystals, characterized by periodic splay modulation, defect structures, and a weakly first-order transition driven by splay instability, expanding understanding of nematic phase diversity.

Contribution

The study introduces a novel splay nematic phase with unique properties and provides a phenomenological theory describing its transition from the uniaxial nematic phase.

Findings

Discovery of a new splay nematic phase with periodic splay modulation.

Observation of defect structures indicating lower symmetry.

Phase transition driven by splay instability, described by Landau-de Gennes theory.

Abstract

Different liquid crystalline phases with long-range orientational but not positional order, so-called nematic phases, are scarce. It rarely occurs that a new nematic phase is discovered and such event is inevitably accompanied by a great interest. Here, we describe a transition from uniaxial to novel nematic phase characterized by a periodic splay modulation of the director. In this new nematic phase, defect structures not present in the uniaxial nematic are observed, which indicates that the new phase has lower symmetry than the ordinary nematic phase. The phase transition is weakly first order with a significant pretransitional behavior, which manifests as strong splay fluctuations. When approaching the phase transition, the splay nematic constant is unusually low and goes towards zero. Analogously to the transition from the uniaxial nematic to the twist-bend nematic phase, this transition is driven by instability towards splay orientational deformation, resulting in a periodically splayed structure. And, similarly, a Landau-de Gennes type of phenomenological theory can be used to describe the phase transition. The modulated splay phase is biaxial and antiferroelectric.