Gel-immobilized single-crystal-like colloidal crystal films

Abstract

Colloidal crystals, three-dimensional periodic arrays of monodisperse colloidal particles, have attracted considerable attention in the field of materials science and for technological applications because of their novel optical applications as photonic crystals. Although polycrystalline colloidal crystals can be easily prepared, the fabrication of a large single crystal is a challenging for advanced studies pertaining to optical properties or applications. This review reports a unique method for fabricating gel-immobilized single-crystal-like colloidal crystal films and their excellent optical properties. A suspension of charged colloids is forced to flow in a flat capillary cell using an air-pulse-drive system. Optical characterizations such as ordinary spectroscopy, laser Kossel diffraction, and imaging spectroscopy for the crystals indicate that the strong shear flow generated in the cell induces a single-domain crystal with a fixed crystallographic orientation determined by the cell geometry. The flow-aligned crystal can be subsequently immobilized in a self-standing hydrogel film by a photopolymerization technique. The resultant gel-immobilized colloidal crystal film can be used as tunable photonic crystals in nonvolatile ionic liquids and be converted into a dry film of densely packed colloidal crystals without cracks. The present materials are expected to contribute to the development of novel colloidal photonic crystals and open the door to industrial mass production of colloidal photonic crystals.