H₂O- and ethanol concentration-responsive polymer/gel inverse opal photonic crystal

Responsive photonic crystals have attracted much attention due to their strong capability to manipulate the propagation of light in the visible region, but it is still a big challenge to invisibility and mechanical stability. Here, the novel Poly(ether sulfone)/Poly(acrylic acid) inverse opal photonic crystals, which have high mechanical stability and can release visible patterns after wetting with water, are discussed. The Poly(ether sulfone)/Poly(acrylic acid) inverse opal photonic crystals are also responsive to the concentration of ethanol, and the structural color response times increase with increasing ethanol concentration. This design uses the selective infiltration, hydrogen bonding and capillary action of solvent to realize the spectral diversity of reflectance. Owing to the high polarity and hydrogen bonding ability of carboxyl groups, water molecules are adsorbed easily by the poly(acrylic acid) gel. Subsequently, the encrypted information is decrypted due to the redshift of the structural color. Because of its lower polarity and hydrogen bonding ability relative to water, ethanol can impede the absorption of solvent by gel. Therefore, the ethanol concentration can be identified based on the structural color response time. Furthermore, reliable information decryption methods make Poly(ether sulfone)/Poly(acrylic acid) inverse opal photonic crystals potentially uesful as trusted encryption devices.