ties. When the sample suspensions are carefully deionized Reflection spectroscopy is used in kinetic analyses of the nuclewith resins for more than three weeks, the f c -value becomes ation and growth processes of colloidal crystals of silica spheres quite low, in the range from 0.0001 to 0.0003, as we have (110 nm in diameter) in exhaustively deionized aqueous suspenreported recently (30).
sions. Sphere concentrations range from 0.001 to 0.0025 in volume
We have observed the process of colloidal crystallization fraction ( f) for the nucleation and 0.0014 to 0.0036 for the crystalin exhaustively deionized and highly diluted aqueous suslization process, respectively. Induction periods are from 1 to 500 pensions through the sharpening of the reflection peak in s and become longer with decreasing sphere concentration. Nuclereflection spectroscopy (15,19). The crystallization process ation rates are 10 03 to 10 3 mm 03 s 01 and increase sharply as sphere was unexpectedly fast. In a previous paper (31), we studied concentration increases. The crystallization process has been observed through the sharpening and the increase of intensity in the colloidal crystallization kinetically by reflection spectrosreflection peaks for the suspension in a test tube, which stands copy and dynamic light-scattering techniques. Nucleation still after being inverted. Crystal growth rates ยฃ range from 2 to 15 rates were 5.6 1 10 04 to 3.2 1 10 03 mm 03 s 01 at sphere mm/s and decrease linearly as the reciprocal sphere concentration concentrations from volume fraction (f) 0.0006 to 0.001. increases. Crystal growth rates represented by the number of unit Crystal growth rates ranged from 2.9 to 20.7 mm/s and incells u also increase as f increases, ranging from 2 to 23 unit cells/ creased substantially as the sphere concentration increased. s. The importance of electrostatic intersphere repulsion through However, reflection spectroscopy measurements have been electrical double layers and of cooperative fluctuation of colloidal performed for only one sample of silica spheres at volume spheres in crystallization processes is supported.