Dual-responsive PU inverse photonic crystal film with high flexibility for anti-counterfeiting

Abstract

Responsive photonic crystals that can change their color under external stimuli have received extensive attention in colorimetric sensing, detection and anti-counterfeiting. In particular, the inverse photonic crystal (IPC) with a macroporous structure is beneficial for the transmission of external stimuli. Herein, inverse photonic crystal films of polyurethane (PU-IPC) with dual responsive character were fabricated by using SiO₂ particles as template followed by a HF etching process. Compared with the conventional hydrogel based IPC films with a reversible volume swelling or shrinking character under stimuli, the PU macro-porous structure shows varied color changes upon soaking in ethanol with different concentrations owing to the stepwise recovery from a collapsed state to an ordered state. Moreover, the PU-IPC film with high flexibility shows excellent mechanochromic property when pre-soaked in ethanol for a while. Based on the dual responsive character, exquisite patterns were fabricated by selective etching or mask methods on it, which could display dynamic colors in ethanol with different concentrations. This dual responsive PU-IPC film has great potential applications in anticounterfeiting.