Glassforming liquid crystalline equimolar mixtures of MHPOBC and fluorinated compounds -- structural, optical, and dielectric properties

TL;DR

This study investigates the structural, optical, and dielectric properties of three new liquid crystalline mixtures combining MHPOBC with fluorinated homologs, revealing their phase behavior, glass formation, and temperature-dependent optical reflection.

Contribution

It introduces novel equimolar liquid crystalline mixtures with detailed characterization of their phases, glass transition, and optical properties, expanding understanding of fluorinated liquid crystal systems.

Findings

All mixtures exhibit smectic A*, C*, and C_A* phases.

Glass of smectic C_A* forms at 225-238 K.

Reflected light wavelength strongly depends on temperature.

Abstract

Three liquid crystalline equimolar mixtures are formulated, each containing the MHPOBC compound and the homolog from the 3FmHPhF6 series with m = 4, 5, and 6. The properties of the mixtures are investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction, electro-optic measurements, and UV-Vis-NIR and dielectric spectroscopies. In all mixtures, the smectic A*, smectic C*, and smectic C$_A$* phases are observed. Each mixture can be supercooled and forms the glass of smectic C$_A$* at 225-238 K. The glass transition temperature decreases with the increasing C$_m$H$_{2m}$ chain length in the 3FmHPhF6 molecule. The tilt angle in the smectic C$_A$* phase reaches 36.5-37.5{\deg}. The selective reflection of light in the visible and near-infrared spectral ranges is observed, with a strong dependence of the reflected light's wavenumber on temperature.