Evaporation driven self-assembly in a levitated nanocolloidal droplet can create a spatially varying photonic band-gap

Abstract

Levitated colloidal droplets can be used to dynamically assemble millimeter sized discs with a photonic bandgap in the visible spectrum. A top-down scheme is proposed to control the bottom-up kinetics of particle assembly in a bid to modulate photonic bandgap of the precipitate.Levitated drops of different colloidal compositions (specified as the number fraction of particles N) are evaporated under different fluxes of laser irradiation (H). The resulting microstructure of the precipitate is quantified using Voronoi tessellation. Micro-reflectance spectroscopy is used to validate the modulation of the photonic bandgap of the synthesized sample.The parametric control of the evaporation dynamics of the levitated droplet changes the kinetics of the microparticle aggregation as validated by Voronoi tessellation of the scanning electron micrographs of the precipitate. Reflectance microscopy of the precipitate’s surface reveals a spatial shift in the Bragg’s peak of reflectance. Mean variation in the ordering of the particles results in the modulation of the bandgap of the precipitate. The simplicity of self-assembly using levitated droplets is shown to be promising pathway for creating samples with spatially tunable photonic bandgap.