(264h) Influence of Defect Microstructure on the Structural Color of Colloidal Films

Self-assembled films of colloidal scale particles can exhibit structural color, intense wavelength-specific reflection derived from geometric diffraction. Due to their lack of dye agents, structural color materials have potential to serve as pigments or sensing materials in chemically degrading environments. While the relationship between colloidal particle length scale and structural color reflection peak wavelength is well studied for self-assembled films, the connection between assembly quality and intensity of color is not. Thickness, crystal defects, and other imperfections impact the perceived color purity of an assembled film. Here, we study this connection by investigating the structural color reflection peak shape as a function of film microstructure via simulation and experiment.

By combining Molecular Dynamics simulations, Transfer Matrix Method calculations, and Finite Difference Time Domain calculations we explore and explain experimental results obtained for evaporative assembly of polystyrene spheres. We find that different commonly observed assembly defects (stacking faults, vacancies, film cracking, etc.) have different magnitudes of effect on colloidal film structural color. Furthermore, we find that films with small quantities of defects may be approximated as multilayer materials. These findings can guide the design of optical materials to tune structural color intensity.