Robust colloidal photonic crystal polymer films for anticounterfeiting

Photonic crystals (PCs) with brilliant structural colors have attracted considerable attention in the field of display and anti‐counterfeiting. Here, free‐standing PC films with antistretching property and invariant brilliant structural colors during compression and deformation were prepared, by combining SiO2 PCs (nSiO2 = 1.46) into polyether sulfone (PES) matrix which has higher refractive index (nPES = 1.68). The excellent physical and chemical stability of the PC films are ascribed to the inherent robust properties of PES resin. In fact, during the stretching, compressing, friction, and bending process, the film retains its structure and optical integrity due to its stable ordered array with constant lattice spacing and effective refractive index. In addition, the appropriate index difference not only contributes to bright structural color, but also enables the PC films to have high transparency. Thus, the pattern in the film can be switched between invisible and visible state under the transformation of weak and strong light. Thereby, the film has great potential in the application of anti‐counterfeiting.