Retention and Deformation of the Blue Phases in Liquid Crystalline Elastomers

TL;DR

This paper reports the synthesis and analysis of liquid crystalline elastomers that retain blue phases, demonstrating their mechanical and optical tunability, which could enable new applications in photonics and sensing.

Contribution

It introduces a method to synthesize elastomers that preserve blue phases and explores their deformation and optical properties under mechanical stress.

Findings

Blue phases are retained in synthesized elastomers.

Lattice periodicity is minimally affected by temperature.

Mechanical deformation causes lattice tilt and red-shift.

Abstract

The blue phases are observed in highly chiral liquid crystalline compositions that nascently organize into a three-dimensional, crystalline nanostructure. The periodicity of the unit cell lattice parameters is on the order of the wavelength of visible light and accordingly, the blue phases exhibit a selective reflection as a photonic crystal. Here, we detail the synthesis of liquid crystalline elastomers (LCEs) that retain blue phase I, blue phase II, and blue phase III. The mechanical properties and deformation of LCEs retaining the blue phases are contrasted to the cholesteric phase in fully solid elastomers with glass transition temperatures below room temperature. Mechanical deformation and chemical swelling of the lightly crosslinked polymer networks induces lattice asymmetry in the blue phase LCE evident in the tuning of the selective reflection. The lattice periodicity of the blue phase LCE is minimally affected by temperature. The oblique lattice planes of the blue phase LCEs tilt and red-shift in response to mechanical deformation. The retention of the blue phases in fully solid, elastomeric films could enable new functional implementations in photonics, sensing, and energy applications.