Bright, non-iridescent structural coloration from clay mineral nanosheet suspensions*

Structural colors originate by constructive interference following reflection and scattering of light from nanostructures with periodicity comparable to visible light wavelengths. Bright and non-iridescent structural colorations are highly desirable, but they were limited to a handful of materials that could hardly be called sustainable.  Here we demonstrate that bright non-iridescence structural coloration easily and rapidly can be achieved from suspended two-dimensional nanosheets of a clay mineral. We show that brightness is enormously improved by using double clay nanosheets, thus optimizing the clay refractive index that otherwise hampers structural coloration from such systems.  Intralayer distances, and thus the structural colors, can be precisely and reproducibly controlled by clay concentration and ionic strength independently, and non-iridescence is readily and effortlessly obtained in this system.  Embedding such clay designed nanosheets in recyclable solid matrices could provide tunable vivid coloration and mechanical strength and stability at the same time, thus opening a new venue for the sustainable penetration of structural coloration to everyday life.