Biomimetic Structural Color Films with a Bilayer Inverse Heterostructure for Anticounterfeiting Applications.

The unique brilliant and angle-independent structural colors of morpho butterfly wings were derived from the multilayer interference, diffraction, and scattering of light with a composite structure including ordered and quasiamorphous arrays. Inspired by the biological heterostructure of ordered and quasiamorphous arrays in the wings, a bilayer inverse heterostructure (BLIHS) containing ordered array layers inverse structure (OALIS) and quasiamorphous array layers inverse structure (Q-AALIS) of polyvinylidene fluoride were successfully prepared through the template method. The BLIHS films selectively displayed iridescent structural color derived from Bragg diffraction of OALIS, whereas the color states transform to noniridescent color because of Q-AALIS just by rotating the sample. Furthermore, the patterning process could be realized by using the spray-coating method on the BILIS films as quasiamorphous array layers. By virtue of this novel photonic structure, the switch between hiding and displaying patterns could be easily realized by changing the viewing angles, and the as-prepared films exhibited inherent excellent durability, which is crucial to their potential for practical applications as anticounterfeiting materials.