We have studied self-assembly of colloidal particles. In this talk, we report on the formation of two-dimensional (2D) diamond-like structures of micron-sized colloidal particles. Positively and negatively charged silica particles of 1 micron in diameter were used. The first layer of negatively charged particles was prepared on a flat, positively charged glass substrate to form non-close-packed 2D colloidal crystals. The second and third layers were then fabricated using the electrostatic adsorption. The position of the adsorbed particles could be controlled by adjusting the zeta potential of the particles and the salt concentration.
Furthermore, we report on the clustering of colloidal particles performed under the microgravity environment of the International Space Station. Colloidal particles were mixed under microgravity and these structures were immobilized in gels cured with ultraviolet (UV) light. Samples returned to the ground were observed under an optical microscope. The space samples had about 50% larger average number of associations and better structural symmetry than the ground control. These findings are expected to be useful for the fabrication of colloidal photonic crystals on the ground.