Bio-inspired transparent structural color film and its application in biomimetic camouflage†
The transparent wings of insects with intelligent structural colors or good invisibility in different surroundings provide them with unique camouflage capability for protection and information exchange. Inspired by the existence of ordered biological nanostructures on the surface of the wings, freestanding composite photonic crystal (PC) films were prepared by infiltrating polydimethylsiloxane (PDMS, n = 1.41) into the interstices of a highly ordered opal PC using poly(methyl methacrylate) (PMMA, n = 1.49) spheres as building blocks. The appropriate refractive index contrast (Δn = 0.08) endowed the composite film with high transparency and vivid structural colors. Consequently, the PC film was invisible in shaded surroundings and showed brilliant structural color under sunlight. Also, 186, 229 and 257 nm PMMA spheres were used to obtain composite PC films with different structural colors. Moreover, as a proof of concept, a biomimetic dragonfly-shaped film was fabricated using a patterned substrate. When it was placed on a green tree under sunlight, abundant structural colors appeared at different specular viewing angles. However, it camouflaged in the environment when the shadows of the green tree shielded the sunlight or when viewed in non-specular angles with sunshine. This unique property indicated their potential applications in biomimetic camouflage and smart stealth materials for bionic machines.