A Robust and Reliable Optical Encryption Film

Reliable anticounterfeiting technologies are crucial for a wide range of industries related to user convenience, safety, and health. Among them, optical anticounterfeiting techniques employing a water infiltration mechanism inspired from <i>Diphylleia grayi</i> have been attracting increasing attention due to its ease of operation, eco-friendliness, and high security. However, there are still challenges, such as slow response times, low reversibility, and insufficient long-term stability. To address these issues, we present a novel optical encryption film that quickly and reliably ensures a reversible transition between opaque (%<i>T</i> ∼0.87%) and transparent states (%<i>T</i> ∼88.5%) upon water infiltration. We fabricate the film through the integration of the micropyramidal hole structure with copolymerized hydrophilic polymer brushes. The microstructures induce structural light scattering in the dry state and also act as an armor to protect the copolymerized polymer brushes under external physical force with durability. The hydrophilic polymer brushes allow rapid water infiltration and evaporation, which results in fast and reversible optical transition. The proposed polymeric encryption film exhibits useful and intriguing demonstration of potential anticounterfeiting applications.