Lattice Transformation-Induced Retroreflective Structural Colors.

Retroreflective structural colors can usually be achieved based on interference combined with a total internal reflection mechanism or diffraction of a monolayer hexagonal two-dimensional (2D) colloidal array. Here, a novel retroreflective structural color was generated based on a hexagonal-parallelogram lattice transformation by stretching 3D photonic crystals with nonclosely packed long-range order. Compared to previous retroreflective colors, this new retroreflective color exhibits two unique off/on color switches: (1) a strain-dependent off/on color switch along the stretching direction and (2) a sample horizontal rotation angle-dependent off/on color switch under the fixed strain. These strain-responsive retroreflective colors are ideal candidates for visually sensing kinesio tapes' strain in practical applications and anticounterfeiting. This work reveals a new structural color regulation mechanism and will advance potential applications in anticounterfeiting, sensing, displays, etc.