What question did this study set out to answer?

To investigate the mechanisms behind electrohydrodynamic instabilities and pattern formation in thin nematic liquid crystal films.

July 12, 2026Journal of Fluid Mechanics0 citations

Electrohydrodynamic nano-patterning in thin nematic films: a multi-scale study on coalescence arrest and surface functionality

PCPrateek ChowdhuryIndian Institute of Technology BHU SCSatyajeet ChoudhuryIndian Institute of Technology BHU DBDebdip BhandaryIndian Institute of Technology BHU

Key Points

To investigate the mechanisms behind electrohydrodynamic instabilities and pattern formation in thin nematic liquid crystal films.
Conducted continuum-scale nonlinear simulations and molecular dynamics simulations.
Identified morphological pathways at varying electric fields and filling ratios.
Performed parametric studies on the interplay of field strength, filling ratio, and anchoring properties.
Low electric fields resulted in no-patterning mode, while critical fields led to columnar mode formation.
Secondary structure mode was observed at low filling ratios, enhancing morphologies with primary columns and droplets.
Simulations revealed potential for diverse applications in photolithography and electro-optic devices.

Abstract

Electrohydrodynamic (EHD) instabilities at the free deformable surface of thin nematic liquid crystal (NLC) films can generate large-area, self-organised, multi-scale surface morphologies under an external electrostatic field. In this work, we present a comprehensive investigation of EHD patterning in thin NLC films combining continuum-scale nonlinear simulations (NS) and molecular dynamics (MD). The multi-scale analysis identifies three principal morphological pathways: (i) no-patterning mode, observed at low electric fields; (ii) columnar mode, emerging above a critical field; and (iii) coalescence mode, characterised by lateral merging of patterns at higher field strengths. The NS further unveil two distinct pathways of the columnar mode – the secondary structure mode (SSM), exhibiting primary columns with secondary droplets; and the primary structure mode, featuring uniformly spaced primary columns. The SSM is favoured at low air-to-NLC filling ratios, where the additional elastic energy requirement to sustain anisotropic interfacial anchoring enhances surface deformation, forming multi-scale morphologies. The MD simulations additionally reveal a fundamental thermodynamic basis of EHD instability, dictating the patterning of NLC. The evolution, transition and tunability of these morphologies are governed by a complex interplay of field strength, filling ratio, anchoring anisotropy, elasticity and dielectric anisotropy. Parametric studies across this design space further offer strategies for tuning the prominence of secondary structures and arresting coalescence. The NS and MD simulations collectively reveal a bimodal orientational anisotropy, demonstrating the pattern’s function as a self-assembled photomask. These findings reveal the rich morphological diversity and surface functionality of NLC films, with promising applications in photolithography, electro-optic devices and adhesive systems.

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