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

Abstract

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