(552e) Reconfigurable Light Diffraction Response of Ellipsoidal Colloids By Electric Field Assisted Assembly

Colloids self-assemble to a variety of crystal structures potentially useful in applications involving structural color materials. However, the fundamental relationship between the quality of the real space crystal structure (microscopic-scale defect microstructure) and the intensity of the light diffraction response (macroscopic-scale) remains poorly understood. In this study, we use alternating current (AC) electric field assisted assembly to produce millimeter-scale arrays of ellipsoidal colloids. Compared to spheres, these particles possess an additional rotational degree of freedom for tailoring the optical/structural properties of the assembly. Small-angle light scattering (SALS) is used to quantify the light diffraction response. The time-resolved SALS probes the kinetics of positional and orientational ordering in the self-assembled anisotropic structures, which have complex symmetry. The ordered colloidal structures are created with polystyrene ellipsoids of aspect ratio 1.8 (major axis 6.85 μm and minor axis 3.85 μm). Here, we show three different light diffraction patterns measured from different real space structures: a phase with neither orientational nor positional order (fluid), a phase with high orientational order (chain-like structure), and a phase with high positional and orientational order (close-packed structure). Differences in peak intensity and peak full-width at half-maximum (FWHM) demonstrate differences in long-range ordering. We then demonstrate methods to improve the quality of the colloidal crystals through optimization of the applied electric-field strength and frequency. We finally present a combined experimental and computational approach to investigate the shape effect on colloids ordering kinetics. This research contributes to the understanding of optical properties of anisotropic colloidal crystals, as is useful for designing the brilliance of structural color at visible and infrared wavelengths.