Monte Carlo Simulation of Smectic Liquid Crystals and the Electroclinic Effect: the Role of the Molecular Shape

TL;DR

This study uses Monte Carlo simulations to investigate how molecular shape influences phase behavior and electroclinic effects in liquid crystals, revealing shape-dependent phases and defect structures.

Contribution

It introduces a simplified model of bent-rod molecules to elucidate the role of molecular shape in liquid crystal phases and electroclinic responses.

Findings

Steric repulsion can induce smectic-C phase without dipole interactions.

Weakly angled molecules exhibit a strong electroclinic effect with ~19° tilt.

Vortex-like defects are observed in the smectic-A phase.

Abstract

Using Monte Carlo simulation methods, we explore the role of molecular shape in the phase behavior of liquid crystals and the electroclinic effect. We study a "bent-rod" mesogen shaped like the letter Z, composed of seven soft spheres bonded rigidly together with no intra-molecular degrees of freedom. For strongly angled molecules, we find that steric repulsion alone provides the driving force for a smectic-C phase, even without intermolecular dipole-dipole interactions. For weakly angled (nearly rod-like) molecules, we find a stable smectic-A (SmA) phase and a strong electroclinic effect with a saturation tilt angle of about 19 degrees. In the SmA phase we find evidence of vortex-like point defects. We also observe a field-induced nematic-smectic phase transition.