Kinetic Analyses of Colloidal Crystallization in a Sinusoidal Electric Field as Studied by Reflection Spectroscopy

The effect of a sinusoidal electric field on crystal growth rates in the colloidal crystallization of silica spheres (110 nm in diameter) in exhaustively deionized aqueous suspensions has been studied by reflection spectroscopy. Sphere concentration is 0.0016 in volume fraction. Nucleation time is shorter than 1 s. The crystal growth rates, v, of the body-centered cubic lattices have been determined from the increase in the cube root of the intensity in the sharpened reflection peaks. The v value is 20 µm/s in the absence of an electric field. v decreases from 20 to 8 µm/s as the voltage applied increases from 0 to 10 V at 1 Hz. v decreases from 30 to 15 µm/s when frequency increases from 0.01 to 10 Hz at E = 6 V, and remains constant irrespective of frequencies higher than 10 Hz up to 10 kHz. Interestingly, the crystallization of bcc lattices is enhanced at low frequencies between 0.01 and 0.5 Hz. The main causes for the retardation of crystallization at high frequencies and voltages are (a) the additional translational fluctuation of the spheres and the surrounding electrical double layers by the electric field, and (b) the partial melting of the crystals by the shearing forces in an electric field. The importance of electrostatic intersphere repulsion resulting from overlap of the electrical double layers and cooperative and synchronized fluctuation of colloidal spheres in crystallization processes is strongly supported. Copyright 1999 Academic Press.