Gel immobilization of centimeter-sized and uniform colloidal crystals formed under temperature gradient

We report the fabrication of large and high-quality charged colloidal crystals that are incorporated in a polymer hydrogel matrix. The colloidal crystals are prepared by the thermally induced unidirectional crystallization of colloidal silica in coexistence with pyridine, whose dissociation degree increases with temperature. Their crystal structures are immobilized in the polymer hydrogel matrix by photoinduced polymerizations. The crystals are large sized (maximum dimensions: 1 x 10 x approximately 30 mm), and their lattice planes are well oriented and parallel to the gel surface. Furthermore, they have excellent spatial uniformity in the Bragg wavelengths (<0.7% in standard deviation). The present gelled colloidal crystals, which are unique in that they have large sizes as well as good optical uniformity, will be useful as photonic materials.