Filling and wetting transitions of nematic liquid crystals on sinusoidal substrates

TL;DR

This paper investigates how nematic liquid crystals exhibit unique wetting and filling behaviors on sinusoidal substrates, revealing that molecular orientation significantly alters transition sequences compared to simple fluids.

Contribution

It demonstrates that the presence of nematic order can suppress or modify filling and wetting transitions, depending on molecular alignment at interfaces and substrates.

Findings

Filling transition may be absent in nematic fluids due to molecular orientation.

Complete wetting transition can be prevented, leading to persistent filled states.

Transitions occur only within narrow substrate amplitude ranges.

Abstract

Close to sinusoidal substrates, simple fluids may undergo a filling transition, in which the fluid passes from a dry to a filled state, where the interface remains unbent but bound to the substrate. Increasing the surface field, the interface unbinds and a wetting transition occurs. We show that this double-transition sequence may be strongly modified in the case of ordered fluids, such as nematic liquid crystals. Depending on the preferred orientation of the nematic molecules at the structured substrate and at the isotropic-nematic interface, the filling transition may not exist, and the fluid passes directly from a dry to a complete-wet state, with the interface far from the substrate. More interestingly, in other situations, the complete wetting transition may be prevented, and the fluid passes from a dry to a filled state, and remains in this configuration, with the interface always attached to the substrate, even for very large surface fields. Both transitions are only observed for a same substrate in a narrow range of amplitudes.