Van der Waals interaction in uniaxial anisotropic media

TL;DR

This paper investigates how the tilt of the optical axis affects van der Waals interactions in uniaxial anisotropic media, deriving general formulas and exploring implications for colloid stability.

Contribution

It introduces a comprehensive theoretical framework for van der Waals forces in anisotropic media with nonzero tilt, including a temperature-dependent dielectric tensor parameterization.

Findings

Tilt influences van der Waals attraction strength.

Solid slabs experience a torque aligning them with the optical axis.

Maximum attraction occurs for homeotropic alignment.

Abstract

Van der Waals interactions between flat surfaces in uniaxial anisotropic media are investigated in the nonretarded limit. The main focus is the effect of nonzero tilt between the optical axis and the surface normal on the strength of van der Waals attraction. General expressions for the van der Waals free energy are derived using the surface mode method and the transfer-matrix formalism. To facilitate numerical calculations a temperature-dependent three-band parameterization of the dielectric tensor of the liquid crystal 5CB is developed. A solid slab immersed in a liquid crystal experiences a van der Waals torque that aligns the surface normal relative to the optical axis of the medium. The preferred orientation is different for different materials. Two solid slabs in close proximity experience a van der Waals attraction that is strongest for homeotropic alignment of the intervening liquid crystal for all the materials studied. The results have implications for the stability of colloids in liquid crystal hosts.