Spectral tuning of gel-immobilized colloidal photonic crystals

Abstract

Colloidal crystals, three-dimensional periodic arrays of monodisperse colloidal particles, have attracted considerable attention owing to their novel optical applications as photonic crystals. In particular, the optical properties of colloidal crystals, immobilized in polymer gels, can be tuned by adjusting the gel volume through an external stimulus. Therefore, these crystals are expected to have applications, e.g., as tunable photonic crystals and biological and chemical sensors for monitoring changes through the optical stop-band wavelength or Bragg reflection color. In this paper, we overview our recent work on gel-immobilized colloidal photonic crystals with high quality including preparation methods and excellent tuning properties. At first, we show that a centimeter-sized single-crystal-like colloidal crystal film can be prepared through use of an air-pulse-drive system. The crystal can be subsequently immobilized in a hydrogel network by a photopolymerization technique without deterioration of crystal quality. Then, tuning by external stimuli, including solvent exchange and temperature change, is demonstrated. In particular, we show that colloidal crystals immobilized in copolymer hydrogels exhibit a variety of tunable behaviors. In addition, we show that ionic liquids, which avoid solvent evaporation, are useful swelling solvents for tuning the optical properties.