Electro-optic properties of giant colloidal crystals

Giant colloidal crystals, 8 mm in the largest dimension have been formed in a test tube of 13 mm in outer diameter in exhaustively deionized and diluted colloidal suspensions. Responses in the colloidal structural changes induced by an alternating electric field (sine- and square-wave fields) have been studied by the reflection-intensity and spectrum measurements of colloidal crystals. Several characteristic modulation effects such as phase difference, changes in the amplitudes, and transformation of waveforms have been observed. Furthermore, generations of the harmonics, harmonic oscillation, and characteristic frequencies are observed for the colloidal crystals. These results support strongly that the electro-optic effects are ascribed to the acoustic shear waves and the synchronous dynamics of colloidal spheres in the crystal lattices.