Photonic Papers and Inks: Color Writing with Colorless Materials

A photonic paper/ink system for color writing on and with colorless materials is described. The “paper” is a 3D crystal of polymer beads embedded in an elastomer matrix made of poly(dimethylsiloxane) (PDMS), and the “ink” is a liquid (e.g., a silicone fluid or organic solvent) capable of swelling the matrix, changing the lattice constant and hence wavelength of light diffracted (see Figure and cover).