Stabilising the Blue Phases

TL;DR

This paper investigates the phase diagram of cholesteric liquid crystals using Landau-de Gennes theory, revealing how elastic constants and temperature-dependent pitch influence the stability of blue phases, especially in systems with helix inversion.

Contribution

It introduces a modified free energy model incorporating all three Frank elastic constants and temperature-dependent pitch, providing new insights into blue phase stability.

Findings

Blue phase stability depends on elastic constants, especially bend and twist.

Large increase in stability region of blue phase I observed.

Qualitative phase diagram change in systems with helix inversion.

Abstract

We present an investigation of the phase diagram of cholesteric liquid crystals within the framework of Landau - de Gennes theory. The free energy is modified to incorporate all three Frank elastic constants and to allow for a temperature dependent pitch in the cholesteric phase. It is found that the region of stability of the cubic blue phases depends significantly on the value of the elastic constants, being reduced when the bend elastic constant is larger than splay and when twist is smaller than the other two. Most dramatically we find a large increase in the region of stability of blue phase I, and a qualitative change in the phase diagram, in a system where the cholesteric phase displays helix inversion.