Casimir forces in modulated systems

TL;DR

This paper derives analytical expressions for electromagnetic fluctuation contributions to the thermodynamics of modulated liquid crystalline films, revealing oscillatory behavior in the Casimir limit that influences wetting and surface phenomena.

Contribution

It provides the first analytical results for electromagnetic fluctuation effects in modulated systems, including explicit formulas for the chemical potential in different regimes.

Findings

Chemical potential oscillates with film thickness in the Casimir limit.

Non-monotonic chemical potential can cause step-wise wetting.

Results applicable to multilayer and modulated soft matter systems.

Abstract

For the first time we present analytical results for the contribution of electromagnetic fluctuations into thermodynamic properties of modulated systems, like cholesteric or smectic liquid crystalline films. In the case of small dielectric anisotropy we have derived explicit analytical expressions for the chemical potential of such systems. Two limiting cases were specifically considered: (i) the Van der Waals (VdW) limit, i.e., in the case when the retardation of the electromagnetic interactions can be neglected; and (ii) the Casimir limit, i.e. when the effects of retardation becomes considerable. It was shown that in the Casimir limit, the film chemical potential oscillates with the thickness of the film. This non-monotonic dependence of the chemical potential on the film thickness can lead to step-wise wetting phenomena, surface anchoring reorientation and other important effects. Applications of the results may concern the various systems in soft matter or condensed matter physics with multilayer or modulated structures.