Multicolor Invisible Patterns Encrypted in Double‐Inverse‐Opal Films Based on Thermally Induced Structural Deformation

Abstract

The integration of invisible photonic patterns into specific micro/nanostructures provides a new way to construct stimuli‐responsive optical anti‐counterfeiting devices. Herein, an innovative strategy for constructing highly invisible patterns in the solvent‐responsive double‐inverse‐opal (DIO) films by the thermal treatment is proposed. The masked area retains the responsive DIO structure, but the exposed area loses the periodic ordered array, which results in different optical responses of the pattern and background to the solvent. Due to the special structure, the scattering effect derived from the randomly distributed polystyrene microspheres within the pores of the inverse‐opal backbone in both the masked area and the exposed area makes the resultant film sample present a pale color, and the encrypted pattern is highly invisible in normal conditions. Interestingly, the hidden pattern can be quickly revealed by ethanol response, showing a large color contrast. Furthermore, reversible bilayer DIO films with multiple hidden patterns for advanced anti‐counterfeiting materials are prepared. Importantly, the as‐prepared film sample can reveal different patterns on the front and back sides in decryption, and simultaneously the overlapping part of the patterns can achieve color mixing based on the bilayer structure, thereby showing great potential in information encryption and anti‐counterfeiting fields.