(510e) Reconfigurable Structural Color By Grating Diffraction in Self-Assembled Colloids

Inspired by the brilliant coloration of natural organisms such as butterflies and chameleons, self-assembled colloidal crystals produce structural color due to light diffraction from their microscale ordering. Differing from the more widely investigated structural color by Bragg reflection, colloids with larger particle size, ~1 µm, show prismatic coloration under conditions of off-axis transmission. This coloration arises due to a grating diffraction mechanism. Here, we study how crystal properties affect optical response and identify the design space for generating reconfigurable structural color by grating diffraction. We self-assemble colloidal arrays in a fluid phase by application of direct current electric fields. Grating diffraction structural color properties of angular dependence, saturation, and brightness depend sensitively on the particle size, layer number and defects. By tuning the current amplitude of the field and the screening length of the solution, we control the resulting phase behavior, grain morphology, and hexatic ordering in ways that lead to interesting coloration behaviors. Both structure and coloration are also tunable by application of different applied voltages. We simulate the self-assembly process by molecular dynamic simulations and correlate the results with experiment. We adopt optical modeling approaches, including the finite-difference time-domain method, to simulate spectral response and identify the operating ranges of the different structural color mechanisms. Taken together, the studies provide insight into grating diffraction structural color as a potential application of self-assembly in technological applications like sensing, camouflage, and coatings.