Theoretical analysis of nanoparticle-induced homeotropic alignment in nematic liquid crystals

TL;DR

This paper provides a theoretical framework explaining how nanoparticles induce a transition from planar to vertical alignment in nematic liquid crystals by altering molecular orientation and elastic properties.

Contribution

It introduces a theoretical model detailing nanoparticle effects on nematic liquid crystal alignment, highlighting long-range coupling and interface modifications.

Findings

Nanoparticles induce local director reorientation near their surface.

Coupling between nanoparticles affects the overall liquid crystal alignment.

Transition from homogeneous to homeotropic alignment is explained theoretically.

Abstract

A theoretical analysis of homeotropic alignment induced by nanoparticles (NPs) in a nematic liquid crystal (NLC) sample cell is presented. It is found that such alignment on the surface of a NP causes a change in the orientation of the molecular director near the surface, which in turn induces variations in the elastic constants and free energy. The induced NLC properties allow coupling between nearby NPs, mediated by the NLC molecules. The rotation of the coupled NPs close to the substrate tends to induce a long-range orientation of the NLC molecular director, leading to modification in the alignment at the interface of NLC and substrate which induces the orientation from homogeneous (planar) to homeotropic (vertical) in the bulk material.