Dynamic control of lattice spacing within colloidal crystals

In this study, we demonstrate reversible changes in lattice spacing within colloidal crystals controlled by an electric field. Crystals are assembled from negatively charged, monodisperse latex particles (945 nm) in an aqueous dispersion, by the application of an alternating electric field (1 kHz, ~35 kV m−1). The lattice spacing within the colloidal crystals is determined by optical microscopy, laser and white light diffraction. Temporary dipoles induced by the electric field cause particles to aggregate into crystal structures; however, electrostatic repulsion prevents adjacent particles touching. One-dimensional (1D) and 2D crystals can be assembled, which act as diffraction gratings with electrically controllable diffraction properties. Two methods of tuning the lattice spacing are presented. In the first method, 1D crystal 'strings' are formed, where the effective lattice spacing is controlled by changing the orientation of the electric field and consequently the orientation of the strings. In the second method, a rotating electric field generates 2D crystals where lattice spacing is controlled by varying the field intensity.