Kinetic Analyses of Colloidal Crystallization in a Wide Range of Sphere Concentrations as Studied by Reflection Spectroscopy

Abstract

The nucleation and growth rates in the colloidal crystallization of silica spheres (103 nm in diameter) from 0.006 to 0.04 in volume fraction (φ) have been measured by reflection spectroscopy. Kinetics of the crystallization has been discussed in a wide sphere concentration range (from φ=0.0005 to φ=0.04) using the data of this work and the previous work (110 nm in diameter) in exhaustively deionized aqueous suspensions. The induction period for nucleation decreases sharply as the sphere concentration increases. The nucleation rate increases substantially from 1×10−3 to 1×107 mm−3 s−1 when φ increases from 0.0005 to 0.04. The crystal growth process consists of the fast growing step toward metastable crystals (rate v1) and slow growth accompanied with the reorientation toward stable ones (rate v2). The v1 values increase first from 5 to 20 μm/s and then turn back to 5 μm/s after passing a maximum. v1 above φ=0.01 remains at 5 μm/s and is insensitive to sphere concentration. The slow step is observed in the high-sphere concentrations only, and v2 decreases sharply from 3 μm/s to 0.7 nm/s when sphere concentration increases from 0.004 to 0.04 in volume fraction. Importance of the electrostatic intersphere repulsion by overlapping of the electrical double layers and the cooperative and synchronized fluctuation of colloidal spheres in the crystallization processes are supported strongly.