Liquid crystal phases with unusual structures and physical properties formed by acute-angle bent-core molecules

TL;DR

This paper investigates the unique phases and physical properties of liquid crystals formed by acute-angle bent-core molecules with a 1,7 naphthalene core, revealing unusual elastic and structural behaviors.

Contribution

It provides detailed characterization of the physical properties and structural phases of ABC liquid crystals, including the discovery of a tetragonal columnar phase with unique elastic properties.

Findings

Small splay elastic constant in uniaxial nematic phase

Formation of a tetragonal columnar phase with uniform uniaxial director

Molecular shape influences elastic and structural properties

Abstract

Liquid crystals formed by acute-angle bent-core (ABC) molecules with a 1,7 naphthalene central core show an intriguing phase behavior with the nematic phase accompanied by poorly understood additional phases. In this work, we characterize the physical properties of an ABC material, such as birefringence, dielectric permittivities, elastic constants, and surface alignment, and present X-ray diffraction and transmission electron microscopy studies of their ordering. The ABC molecular shape resembling the letter $\lambda$ yields a very small splay elastic constant in the uniaxial nematic phase and results in the formation of a tetragonal positionally ordered columnar phase consisting of molecular columns with a uniform uniaxial director that can be bent but not splayed.