Resonant carbon K-edge soft x-ray scattering from lattice-free heliconical molecular ordering: soft dilative elasticity of the twist-bend liquid crystal phase

TL;DR

This study reveals that the twist-bend liquid crystal phase exhibits a lattice-free heliconical structure with temperature-dependent pitch and remarkable elastic softness, as shown by resonant x-ray scattering.

Contribution

It demonstrates the presence of a lattice-free heliconical nematic structure with elastic properties in the twist-bend liquid crystal phase using resonant x-ray scattering.

Findings

Heliconical structure has spatial periodicity without electron density modulation.

The helix pitch varies with temperature and exhibits elastic softness.

Scattering from the helix disappears in the higher temperature nematic phase.

Abstract

Resonant x-ray scattering shows that the bulk structure of the twist-bend liquid crystal phase, recently discovered in bent molecular dimers, has spatial periodicity without electron density modulation, indicating a lattice-free heliconical nematic precession of orientation that has helical glide symmetry. In situ study of the bulk helix texture for the dimer CB7CB shows an elastically-confined temperature-dependent minimum helix pitch, but a remarkable elastic softness of pitch in response to dilative stresses. Scattering from the helix is not detectable in the higher temperature nematic phase.