Nanoporous polymeric photonic crystals by emulsion holography

Abstract

We report the holographic photopatterning of a microemulsion with a formamide polar phase and an acrylate monomer-containing nonpolar phase to produce polymer structures with periodic nanoscale porosity. Formamide is a highly polar solvent that forms well dispersed, nonaqueous emulsion droplets within the monomer-containing nonpolar phase before holographic patterning. Photochemically initiated polymerization of the nonpolar phase generates ordered structures defined by the holographic interference. Evaporation of the formamide from this lamellar structure yields a multilayered stack that acts as a photonic crystal (PC) with high optical reflectivity and a wide reflection bandwidth. The size of formamide droplets in the photopolymer fluid must be controlled to have a narrow distribution and peak near 60 nm to fabricate PC with high reflectivity. Addition of a sodium dioctyl sulfosuccinate (AOT) surfactant helps to stabilize the formamide microemulsion which further facilitates the formation of ordered nanopores with a uniform size.