Kinetic Study on the Colloidal Crystallization of Silica Spheres in the Highly Diluted and Exhaustively Deionized Suspensions as Studied by Light-Scattering and Reflection Spectroscopy

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Static (SLS) and dynamic light-scattering (DLS) measurements and reflection spectroscopy are made for the kinetic analyses of the growing processes of colloidal crystals of silica spheres (103 and 110 nm in diameter) in highly diluted and exhaustively deionized aqueous suspensions. Changes in the SLS curves demonstrate that there exists an induction period in the nucleation process, which is prolonged with decreasing sphere concentration. Induction periods observed from DLS measurements are from 1 to 21 min, and also increase as sphere concentration decreases. The diffusion coefficients of colloidal spheres in the super-saturated liquids and crystal-like structures are estimated to be 1 × 10−12and 5–10 × 10−12m2/s, respectively, which are smaller and larger than the diffusion coefficient of the independent sphere evaluated using the Stokes–Einstein equation, 4.36 × 10−12m2/s. Nucleation rates are 5.6 × 10−4to 3.2 × 10−3mm−3s−1at φ = 0.0006 to 0.001 from the DLS and reflection spectroscopy. The crystal growing process is beautifully explained by the classical diffusion theory of crystallization, though the restricted diffusion of the reacting spheres like as the fused metal systems should be taken into account. Crystal growth rates range from 2.9 to 20.7 μm/s and increase substantially as the sphere concentration increases. The importance of the electrostatic intersphere repulsion through the electrical double layers and the cooperative fluctuation of colloidal spheres in the crystallization processes is supported strongly.