Structure of the twist-bend nematic phase with respect to the orientational molecular order of the thioether-linked dimers

TL;DR

This study investigates the molecular orientation and dipole interactions in nematic and twist-bend nematic phases of liquid crystal dimers using IR absorbance analysis, revealing temperature-dependent order changes and biaxiality emergence.

Contribution

It provides new insights into the orientational molecular order and dipole interactions specific to the twist-bend nematic phase of thioether-linked liquid crystal dimers.

Findings

Long axis orientational order increases as temperature decreases in nematic phase

Biaxial ordering occurs and grows in the twist-bend nematic phase

Dipole absorbance decreases at the nematic-twist-bend transition

Abstract

An analysis of the IR absorbance for the segmented functional groups of liquid crystal dimers: mesogen and linker, enabled the orientation order to be determined and information about the dipole interactions in the nematic and twist-bend nematic phases to be obtained. The long axis orientational order increases as the temperature decreases in the nematic phase, although much more slowly than for the classical nematics, and then reverses this trend in the twist-bend nematic phase due to the tilt of the molecules. In the nematic phase, the short axis of the molecule performs an isotropic uniform rotation and has a uniaxial alignment. In the twist-bend nematic phase, however, biaxial ordering occurs and grows significantly in accordance with the helical deformation of the director. Changes in the mean absorbance in the twist-bend nematic phase were observed: a decrease for the longitudinal dipole at the nematic-twist-bend nematic phase transition, thus emphasizing the antiparallel axial interaction of the dipoles, while the absorbance of the transverse dipoles remains unchanged up to 340 K, and then the latter become parallelly correlated.