LARGE SINGLE-CRYSTALS OF COLLOIDAL SILICA SPHERES APPEARING IN DEIONIZED AND DILUTED SUSPENSION

Close-up color photographs are taken for crystallites (single crystals surrounded by the grain boundaries) in the colloidal crystals of monodisperse silica spheres (diameter: 110 nm +/- 4.5 nm (standard deviation)). Very large crystallites (3 approximately 4 mm) are observed with the naked eye (for the first time) for the completely deionized ana diluted suspensions. Deionization is carefully made with the mixed beds of ion-exchange resins more than 2 weeks old. Size of the crystallites increases sharply as the concentration of spheres decreases, and becomes small at the concentrations slightly higher than the critical concentration of melting toward liquid-like structure. Shape of the crystallites, i.e., mixture of triangle, cubic, pentagonal, hexagonal, cone-like, etc., is recognized in the photographs.