The prediction and design of bio-inspired structural colors using colloidal glasses

Many species of birds display structural colors that arise from the constructive interference of light that is scattered from the internal structure of the feathers. In blue Cotinga birds, the colors are independent of the angle between light source and observer owing to the glassy arrangement of air spheres in keratin in the feather barb (E. R. Dufresne et al, Soft Matter, 2009, 5, 1792-1795). Such colors can be mimicked in colloidal glasses, but while the locations of the peaks in reflectance spectra are accurately predicted by single-scattering models, weak multiple scattering also contributes to the reflected intensity. We develop a model that quantitatively predicts the reflectance spectra of colloidal glasses. To model the multiple scattering, we use a Monte Carlo approach to simulate photon trajectories. We find good agreement between experimental reflectance spectra and the model. We also develop an optimization algorithm to find the parameters required to make specific colors and explore the range of hues that can be achieved with colloidal glasses.