‘Crystal-like’ structure of colloidal spheres in an alternating electric field

Abstract

Changes in lattice structure induced by an alternating electric field (using sine- and square-wave fields) have been studied by time-resolved reflection and transmitted-light spectrum measurements of monodisperse polystyrene spheres (diameter 91 nm) in deionized solution. The spectrum peak shifts to longer or shorter wavelengths depending on the polarity of the electric field. The transformation of the lattice structure on applying a voltage has at least two relaxation times. Fast and slow steps correspond to the structural relaxation and the relaxations of grain boundaries or crystallites, respectively. The wave-forms of the reflection and absorption signals and their Fourier spectra are clarified between 0.3 and 600 Hz with a sine- or square- wave electric field. The results support the idea that the electrostatic intersphere repulsion in the effective hard-sphere model is essential for ordering.