GIANT COLLOIDAL SINGLE-CRYSTALS OF POLYSTYRENE AND SILICA SPHERES IN DEIONIZED SUSPENSION

Shape and size of colloidal single crystals of polystyrene and silica spheres ranging from 81 to 212 nm in diameter (d) are studied mainly with close-up color photographs in the diluted and exhaustively deionized suspensions with ion-exchange resins. Two kinds of single crystals, (1) block-like crystals grown up from the homogeneous nucleation mechanism in the bulk phase far from the cell wall and (2) pillar-like ones from the heterogeneous nucleation along the cell wall, are observed clearly. Size of the colloidal single crystals is very large (3-8 mm) at the sphere concentration slightly higher than the critical concentration of melting (phi(c)). Phi(c)-Values are around 0.0002 in volume fraction irrespective of sphere diameter ranging from 90 to 210 nm, and much higher for the spheres smaller than 90 nm, e.g., 0.0036 and 0.0014 for colloidal silica (CS-61, d = 81 nm) and polystyrene spheres (D1C25, 85 nm), respectively. Crystal size decreases very sharply as sphere concentration increases, since the number of nuclei increases substantially with sphere concentration.