Thermotropic Nematic and Smectic Order in Silica Glass Nanochannels

TL;DR

This study investigates how liquid crystal orderings behave when confined in silica nanochannels, revealing continuous transitions and the influence of disorder, contrasting with bulk phase behaviors.

Contribution

It provides the first detailed comparison of thermotropic nematic and smectic order in nanochannels using optical birefringence and Landau-de-Gennes analysis.

Findings

Transitions are continuous in confinement, unlike bulk.

Smectic order is more affected by disorder than nematic.

Both orders are influenced by wall-imposed fields.

Abstract

Optical birefringence measurements on a rod-like liquid crystal (8OCB), imbibed in silica channels (7 nm diameter), are presented and compared to the thermotropic bulk behavior. The orientational and positional order of the confined liquid evolves continuously at the paranematic-to-nematic and sizeably broadened at the nematic-to-smectic order transition, resp., in contrast to the discontinuous and well-defined second-order character of the bulk transitions. A Landau-de-Gennes analysis reveals identical strengths of the nematic and smectic ordering fields (imposed by the walls) and indicates that the smectic order is more affected by quenched disorder (originating in channel tortuosity and roughness) than the nematic transition.