Fluctuations in confined nematic liquid crystals in a regime of critical wetting

TL;DR

This paper investigates how surface interactions influence fluctuation modes in confined nematic liquid crystals near critical wetting, revealing distinct behaviors of uniaxial and biaxial modes and their critical softening close to phase coexistence.

Contribution

It provides a theoretical analysis of fluctuation spectra in nematic liquid crystals near critical wetting, highlighting the impact of surface free-energy potentials on local director modes.

Findings

Bound biaxial fluctuation modes appear with strong surface suppression.

Uniaxial local excitations are promoted by surface-enhanced order.

Fluctuation spectra soften and develop cusps near the critical temperature.

Abstract

Within the macroscopic Landau-de Gennes approach, we examine the Gaussian normal mode fluctuations of semi-infinite nematic liquid crystals in a regime of critical wetting. It is argued that surface free-energy potentials that strongly suppress the long-range nematic order favor the appearance of bound biaxial nematic-director fluctuation modes, located in the domain occupied by the thermodynamic phase wetting the wall. Instead, substrates enhancing the orientational order promote the existence of uniaxial nematic-director local excitations. Close to the phase coexistence temperature both types of local exciations are strongly softened as compared to their bulk counterparts and acquire characteristic cusplike low-energy spectra. These spectrum peculiarities are directly connected to the critical behavior of the mean-field interface position and can provide a valuable insight on the nature of surface interactions and critical wetting phenomena in nematic liquid crystals. Possible changes in the local director mode properties resulting from the critical interface position fluctuations and order electricity effects are also discussed.