Columnar versus smectic order in systems of charged colloidal rods

TL;DR

This study analyzes the stability of various liquid crystalline phases in charged rod systems, revealing how screening length influences the transition between nematic, smectic, and columnar states through theoretical and simulation methods.

Contribution

It provides a bifurcation analysis of phase stability in charged rods, highlighting the role of Debye screening length in phase transitions, supported by Brownian dynamics simulations.

Findings

Nematic-smectic transition occurs before nematic-columnar at strong screening.

Hexagonal columnar order remains stable at larger screening lengths.

Simulation results support the theoretical phase stability predictions.

Abstract

We study the stability of inhomogeneous liquid crystalline states in systems of monodisperse, stiff, charged rods. By means of a bifurcation analysis applied to the Onsager free energy for charged rods in strongly nematic states, we investigate nematic-smectic and nematic-columnar instabilities as a function of the Debye screening length. While the nematic-smectic transition clearly pre-emts the nematic-columnar one in the regime of strong screening a marked stability of hexagonal columnar order is observed at larger screening lengths. The theoretical results are substantiated by Brownian dynamics computer simulation results based on the Yukawa-site model. Our findings connect to experiments on tobacco mosaic virus rods in particular but might be relevant for soft rod-like mesogens in strong external directional fields in general.