Chiral phase-coexistence in compressed double-twist elastomers

TL;DR

This paper models the behavior of double-twist liquid crystal elastomers under compression, revealing phase coexistence and strain-straightening phenomena, with implications for biological systems like collagen fibrils.

Contribution

It extends anisotropic rubber elasticity theory to describe phase coexistence in compressed double-twist elastomers, including exact solutions in certain limits.

Findings

Coexistence of high and low twist phases under compression.

Strain-straightening observed in extension with exact formulas.

Coexistence persists at small strains and is experimentally relevant.

Abstract

We adapt the theory of anisotropic rubber elasticity to model cross-linked double-twist liquid crystal cylinders such as exhibited in biological systems. In mechanical extension we recover strain-straightening, but with an exact expression in the small twist-angle limit. In compression, we observe coexistence between high and low twist phases. Coexistence begins at small compressive strains and is robustly observed for any anisotropic cross-links and for general double-twist functions -- but disappears at large twist angles. Within the coexistence region, significant compression of double-twist cylinders is allowed at constant stress. Our results are qualitatively consistent with previous observations of swollen or compressed collagen fibrils, indicating that this phenomenon may be readily accessible experimentally.