Kinetic Analyses of the Colloidal Crystallization of Silica Spheres As Studied by Reflection Spectroscopy
Reflection spectroscopy is used in kinetic analyses of the nucleation and growth processes of colloidal crystals of silica spheres (110 nm in diameter) in exhaustively deionized aqueous suspensions. Sphere concentrations range from 0.001 to 0.0025 in volume fraction (phi) for the nucleation and 0.0014 to 0.0036 for the crystallization process, respectively. Induction periods are from 1 to 500 s and become longer with decreasing sphere concentration. Nucleation rates are 10(-3) to 10(3) &mgr;m-3 s-1 and increase sharply as sphere concentration increases. The crystallization process has been observed through the sharpening and the increase of intensity in the reflection peaks for the suspension in a test tube, which stands still after being inverted. Crystal growth rates v range from 2 to 15 &mgr;m/s and decrease linearly as the reciprocal sphere concentration increases. Crystal growth rates represented by the number of unit cells u also increase as phi increases, ranging from 2 to 23 unit cells/s. The importance of electrostatic intersphere repulsion through electrical double layers and of cooperative fluctuation of colloidal spheres in crystallization processes is supported. Copyright 1997Academic Press
Okubo
T
Department of Applied Chemistry, Gifu University, Gifu, 501-11, Japan
Okada
S