Nematic Films at Chemically Structured Surfaces

TL;DR

This paper presents a theoretical study of nematic film morphology on chemically patterned surfaces, introducing an effective interfacial model that predicts substrate-induced undulations and their scaling behavior, validated by numerical simulations.

Contribution

It develops an exactly-solvable interfacial model for nematic films on patterned substrates, linking interface deformation to surface patterning and film thickness, with semi-quantitative agreement with full Landau-de Gennes simulations.

Findings

Substrate patterns induce strong nematic-air interface deformations.

Undulation amplitude increases with decreasing film thickness and increasing pattern pitch.

A universal scaling function describes interfacial deformation across regimes.

Abstract

We investigate theoretically the morphology of a thin nematic film adsorbed at flat substrate patterned by stripes with alternating aligning properties, normal and tangential respectively. We construct a simple "exactly-solvable" effective interfacial model where the liquid crystal distortions are accounted for via an effective interface potential. We find that chemically patterned substrates can strongly deform the nematic-air interface. The amplitude of this substrate-induced undulations increases with decreasing average film thickness and with increasing surface pattern pitch. We find a regime where the interfacial deformation may be described in terms of a material-independent universal scaling function. Surprisingly, the predictions of the effective interfacial model agree semi-quantitatively with the results of the numerical solution of a full model based on the Landau-de Gennes theory coupled to a square-gradient phase field free energy functional for a two phase system.