Structural coloration of materials can be reconfigured by manipulating the orientation of shape anisotropic building blocks. We demonstrate that cyclic application of electric fields switches the optical response of discoid colloidal liquid crystals through microparticle alignment. 4-µm sulfate-modified polystyrene discoids are self-assembled into a monolayer crystal in an isopropanol-water mixture held between two conductive coverslips with a 120-µm separation. After sedimentation, the discoid minor axes are perpendicular to the substrate (homeotropic alignment). Adding an AC electric field (1 kHz) of ≥ 0.50 V switches the minor axes parallel to the substrate (planar alignment) with high fidelity within ~100 s. Switching off the AC field orients the discoids back into the homeotropic alignment within ~300 s. Kinetic modelling based on the torques induced by electric fields and gravity (for discoids in contact with the substrate) provides good agreement with the measured time constants for both switching directions. This cyclic field application generates reconfigurable structural color in the discoid crystals; its diffraction efficiency shows significant shifts in the peak wavelength and dispersion, consistent with the simulated optical response of the imaged self-assembled discoids. We further extend this electric field-based orientational control to ellipsoids using coplanar multi-fold electrodes. By manipulating the rotational frequency and electric field properties (field strength and frequency), we search for conditions which dynamically switch the alignment of ellipsoids in the liquid crystal structure along different orientations. These temporally and spatially cyclic applications of electric fields provide a promising avenue to reconfigure the structure and functional properties of colloidal crystals assembled from simple dielectric spheroids.
