Optical manipulation of sessile droplets of nematic liquid crystalline materials on the surface of a photovoltaic crystal

TL;DR

This study explores how laser irradiation influences sessile nematic liquid crystal droplets on a photovoltaic crystal surface, revealing electric field-driven behaviors like merging, jetting, and disintegration in both nematic and isotropic phases.

Contribution

It demonstrates the manipulation of liquid crystalline droplets using electric fields generated by photovoltaic effects, a novel approach for controlling soft matter with light and electric fields.

Findings

Laser irradiation causes droplet merging and filament formation.

Laser focus induces droplet disintegration via jet streams.

Effects occur in both nematic and isotropic phases.

Abstract

We investigated the effects of laser irradiation on sessile droplets of three well-known liquid crystalline 12 materials (5CB, 8CB, E7) deposited on the surface of an iron-doped lithium niobate (LN:Fe) crystal. The static electric 13 field, which is generated via the bulk photovoltaic effect in the LN:Fe substrate, produces the merging of smaller 14 droplets into filaments oriented in the radial direction with respect to the laser spot. It also induces filament jetting 15 from the rim of larger droplets toward the center of the illumination area. When the laser beam is focused directly 16 onto the larger droplets, they abruptly disintegrate via the formation of several jet streams. The described effects are 17 present in the nematic and also in the isotropic phase. We attribute them to a large gradient of the surface electric field 18 that produces driving forces via the induced dipole moments of the droplets, analogous to electric field-based droplets 19 transport mechanisms known for standard dielectric liquids.