(105h) Disordering Colloidal Crystals and Directing Structural Color

Structural color is a property emerging from the colloidal self-assembly of thin films. Light scattered by such microstructured surfaces experiences constructive interference and results in color which depends exclusively on the local order of the colloidal crystals. Assemblies of the highest quality still contain defects which impact the intensity of the reflected light. We examined this impact by investigating order-to-disorder transitions in monolayers of colloidal particles packed by Langmuir-Blodgett deposition, and in colloidal crystals obtained by solvent evaporation. We programmed the number of defects by introducing known ‘impurities’ in the form of anisotropic ‘dumbbell’ and rod-like particles and interpreted the results via optical and electron microscopy. Increasing the volume fraction of dumbbell particles as well as suppressing electrostatic repulsion with salt come with a quantifiable disordering of the hexagonally packed monolayer. Similarly, adding nanorods to the thin crystal film is a tunable way of disordering the local arrangement of nanospheres resulting in the controlled degradation of structural color. Compared to introducing defects by spherical polydispersity, rod-like impurities appear to be more effective in changing optical properties of colloidal crystal due to their additional rotational degrees of freedom. These findings relate uniquely to shape anisotropy and are indifferent of material, and as such may improve our toolbox for designing metastable structures with unusual optoelectronic properties.