Waves at surfactant-laden liquid-liquid crystal interface

TL;DR

This paper provides a theoretical analysis of surface waves at a surfactant-covered liquid-liquid crystal interface, deriving dispersion relations and identifying modes influenced by anisotropy and anchoring effects.

Contribution

It introduces a comprehensive theoretical model for surface waves at nematic-liquid interfaces with surfactants, including anisotropic effects and director relaxation modes.

Findings

Dispersion relations similar to isotropic systems but with anisotropic viscosity.

Identification of additional modes related to nematic director relaxation.

Potential application in experimental determination of interface properties.

Abstract

A theoretical study is presented of surface waves at a monomolecular surfactant film between an isotropic liquid and a nematic liquid crystal for the case when the surfactant film is in the isotropic two-dimensional fluid phase and induces homeotropic (normal to the interface) orientation of the nematic director. The dispersion relation for the surface waves is obtained, and different surface modes are analyzed with account being taken of the anchoring induced by the surfactant layer, the curvature energy of the interface, and the anisotropy of the viscoelastic coefficients. The dispersion laws for capillary and dilatational surface modes retain structure similar to that in isotropic systems, but involve anisotropic viscosity coefficients. Additional modes are related to relaxation of the nematic director field due to anchoring at the interface. The results can be used to determine different properties of nematic-surfactant-isotropic interfaces from experimental data on surface light scattering.