The isotropic-cholesteric transition in liquid-crystalline gels

TL;DR

This paper investigates the isotropic-cholesteric transition in chiral nematic gels, revealing how elastic compatibility influences the formation of a conical helix and affects the phase transition and sample shape.

Contribution

It introduces a model showing the formation of a conical helix as an energy-minimizing structure balancing elongation and twisting in chiral nematic gels.

Findings

Conical helix minimizes energy by balancing elongation and twisting.

Helical cone angle and pitch depend on chirality strength.

Sample shape changes at the isotropic to cholesteric transition.

Abstract

In a nematic gel, the appearance of nematic order is accompanied by a spontaneous elongation of the gel parallel to the nematic director. If such a gel is made chiral, it has a tendency to form a cholesteric helical texture, in which local elongation of the gel parallel to the nematic director is suppressed due to the requirement of elastic compatibility. We show that a conical helix in which the director makes an oblique angle with respect to the helix axis serves as an energy minimizing compromise between the competing tendencies for elongation and twisting. We find the dependence of the helical cone angle and pitch on the strength of the chirality, and determine the change in sample shape at the isotropic to cholesteric phase transition.