Toward 4D printing with structural colors

The colors in the world around us are produced through either absorption of light by molecules (pigmentary colors) or scattering of light by nanostructures (structural colors). Nature provides many spectacular examples of structural colors—the bright colors of some butterflies, beetles, fish or birds (think peacocks) are due to nanostructures that cause the reflected light waves to overlap. Structural coloration occurs on surfaces with a nanostructure with dimensions similar to those of the wavelength of the incident light (typically below a micron). These ordered nanostructures are known as photonic crystals.