Characterization of the sub-micrometer hierarchy levels in the twist-bend nematic phase with nanometric helices via photopolymerization. Explanation for the sign reversal in the polar response

TL;DR

This study uses photopolymerization and SEM imaging to reveal hierarchical sub-micrometer structures in the twist-bend nematic phase, explaining the sign reversal in polar response through director tilting.

Contribution

It provides direct visualization of nanometric helices and hierarchical structures in the twist-bend nematic phase, linking these features to electro-optical behavior.

Findings

Hierarchical nanostructures from tens of nanometers to micrometers are visualized.

Submicron features consistent with previous X-ray data are directly observed.

Tilted director field in self-deformation stripes explains sign reversal in polar response.

Abstract

Photo-polymerization of a reactive mesogen mixed with a mesogenic dimer, shown to exhibit the twist-bend nematic phase ($N_{TB}$), reveals the complex structure of the self-deformation patterns observed in planar cells. The polymerized reactive mesogen retains the structure formed by liquid crystalline molecules in the twist bend phase, thus enabling observation by Scanning Electron Microscope (SEM). Hierarchical ordering scales from tens of nanometers to micrometers are imaged in detail. Submicron features, anticipated from earlier X-ray experiments, are visualized directly. In the self-deformation stripes formed in the $N_{TB}$ phase, the average director field is found tilted in the cell plane by an angle of up to 45$^{\circ}$ from the cell rubbing direction. This tilting explains the sign inversion being observed in the electro-optical studies.