Structural color palette of disordered colloids in the Rayleigh scattering regime

Abstract: Structural coloration by Rayleigh scattering is widespread in nature and holds a prominent place in various art objects over a broad period of time, from ancient Chinese porcelains to Renaissance paintings. Beyond the common statement that Rayleigh scattering is the primary mechanism behind the multiple colored appearances of the sky, it appears that the relationship between material parameters and the colors that appear in different observation conditions has not been thoroughly explored so far. The present study aims to offer a general overview of the structural colors accessible by Rayleigh scattering as a function of the material parameters, alongside a scalable and environment-friendly process to realize solid composite materials with targeted structural colors in reflection and transmission. Monte Carlo light transport simulations are performed to compute the structural color palette of disordered colloids -- dielectric particles in a nonscattering matrix -- in different observation modes. In particular, we provide a range of physical parameters in which the materials exhibit the same blue color in diffuse reflection and transmission. We also show that, as may be counterintuitive at first, the addition of black absorbents to the matrix of a white (opaque) material can lead to the emergence of a blue coloration in diffuse reflection, thanks to the interplay between multiple light scattering and light absorption. These predictions are validated by optical experiments on colloidal suspensions of Yttria-stabilized Zirconia (ZrO$_2$:Y$_2$O$_3$) nanoparticles in aqueous solutions. The potential of Rayleigh-scattering materials for visual arts and design is further supported by realizing solid-state composites based on abundant materials, namely borosilicate clays and hybrid silica-based glasses, using soft chemistry at room temperature.