Mechano-Chromic Photonic Crystals with Substrate-Independent Brilliant Colors for Visual Sensing and Anti-Counterfeiting Applications

The mechano-chromic photonic crystals (MPCs) show self-restricted applications because they only exhibit bright reflective color on the black substrates but dim, complex, or white colors on substrates with different colors due to the superposition of incoherent scattering of light from MPCs and substrates. Herein, MPCs with substrate-independent brilliant reflective colors, highly ordered structures, and superior mechano-chromic performances are fabricated through the co-assembly of same size silica and silica-polydopamine (PDA) particles into the polymers. The silica-PDA particles can efficiently absorb the harmful incoherent scattering of lights but show negligible effects on the long-range order and thus endow MPCs with highly brilliant colors regardless of substrates. Compared to conventional MPCs, the as-fabricated MPCs exhibit brilliant reflective colors on the white substrates at relaxing and stretching states, showing their great potential as real visual sensors. Moreover, based on the characteristics of MPCs, double-layer photonic patterns with the color-independent properties of each side at pristine states, showing diverse changes of colors on both sides upon stretching, are prepared and can be used for anti-counterfeiting.