Colloidal particles at a nematic-isotropic interface: effects of confinement

TL;DR

This study investigates how colloidal particles interact with a nematic-isotropic liquid crystal interface, revealing complex particle trajectories and interface structures influenced by confinement and interface shape.

Contribution

It combines experimental observations with numerical modeling to analyze particle-interface interactions and the effects of confinement in nematic liquid crystals.

Findings

Particles are captured and dragged by the interface, forming periodic structures.

Interface shape influences particle trajectories, especially near wedge-like regions.

Numerical models qualitatively match experimental interface structures and forces.

Abstract

When captured by a flat nematic-isotropic interface, colloidal particles can be dragged by it. As a result spatially periodic structures may appear, with the period depending on a particle mass, size, and interface velocity~\cite{west.jl:2002}. If liquid crystal is sandwiched between two substrates, the interface takes a wedge-like shape, accommodating the interface-substrate contact angle and minimizing the director distortions on its nematic side. Correspondingly, particles move along complex trajectories: they are first captured by the interface and then `glide' towards its vertex point. Our experiments quantify this scenario, and numerical minimization of the Landau-de Gennes free energy allow for a qualitative description of the interfacial structure and the drag force.