Photonic papers: Colloidal crystals with tunable optical properties

This paper demonstrates the fabrication of colloidal crystals with tunable optical properties and their utilization as photonic papers for displaying colored letters and patterns. In a typical procedure, monodispersed spherical colloids were assembled into a three-dimensional crystal, followed by infiltration and curing of an elastorner such as poly(dimethylsiloxane). When an ink (i.e., any liquid capable of swelling the elastomer) was applied to the surface of this crystal, the lattice constant (and thus the color of Bragg-diffracted light) was changed. If the difference between the colors of the initial and final states is sufficiently large to be distinguishable by the naked eye, this system can be used to write and print colored patterns with an edge resolution as high as similar to50 mum.