Cholesteric and screw-like nematic phases in systems of helical particles

TL;DR

This study investigates how boundary conditions affect the formation of cholesteric and screw-like nematic phases in systems of helical particles, revealing that confinement promotes cholesteric phases without destabilizing screw-like phases.

Contribution

It demonstrates that removing periodic boundary conditions enables cholesteric phases to form, while screw-like phases remain stable, clarifying phase behavior under realistic confinement.

Findings

Cholesteric phase forms with helical axis perpendicular to walls under confinement.

Screw-like nematic phase remains stable despite boundary condition changes.

Boundary conditions influence the type of nematic phase observed in helical particle systems.

Abstract

Recent numerical simulations of hard helical particle systems unveiled the existence of a novel chiral nematic phase, termed screw-like, characterised by the helical organization of the particle C$_2$ symmetry axes round the nematic director with periodicity equal to the particle pitch. This phase forms at high density and can follow a less dense uniform nematic phase, with relative occurrence of the two phases depending on the helix morphology. Since these numerical simulations were conducted under three-dimensional periodic boundary conditions, two questions could remain open. Firstly, the real nature of the lower density nematic phase, expected to be cholesteric. Secondly, the influence that the latter, once allowed to form, may have on the existence and stability of the screw-like nematic phase. To address these questions, we have performed Monte Carlo and molecular dynamics numerical simulations of helical particle systems confined between two parallel repulsive walls. We have found that removal of the periodicity constraint along one direction allows a relatively-long-pitch cholesteric phase to form, in lieu of the uniform nematic phase, with helical axis perpendicular to the walls while the existence and stability of the screw-like nematic phase are not appreciably affected by this change of boundary conditions.