High-resolution dielectric study reveals pore size-dependent orientational order of a discotic liquid crystal confined in tubular nanopores

TL;DR

This study uses high-resolution dielectric measurements to investigate how pore size influences the orientational order of a discotic liquid crystal confined in nanopores, revealing continuous phase transitions and pore-dependent ordering.

Contribution

It demonstrates that dielectric spectroscopy can effectively probe the pore size-dependent orientational order of discotic liquid crystals in nanoporous materials, providing new insights into their phase behavior.

Findings

Radial molecular arrangement on pore walls

Continuous isotropic-to-columnar transition in confinement

Transition temperature shifts with pore size

Abstract

We report a high-resolution dielectric study on a pyrene-based discotic liquid crystal (DLC) in the bulk state and confined in parallel tubular nanopores of monolithic silica and alumina membranes. The positive dielectric anisotropy of the DLC molecule at low frequencies (in the quasi-static case) allows us to explore the thermotropic collective orientational order. A face-on arrangement of the molecular discs on the pore walls and a corresponding radial arrangement of the molecules is found. In contrast to the bulk, the isotropic-to-columnar transition of the confined DLC is continuous, shifts with decreasing pore diameter to lower temperatures and exhibits a pronounced hysteresis between cooling and heating. These findings corroborate conclusions from previous neutron and X-ray scattering experiments as well as optical birefringence measurements. Our study also indicates that the relative simple dielectric technique presented here is a quite efficient method in order to study the thermotropic orientational order of DLC based nanocomposites.