Polychromatic Anti‐Counterfeiting Enabled by Modulus Programming in Blue Phase Liquid Crystal Elastomer Films

Abstract Responsive and easy‐to‐fabricate anti‐counterfeiting devices are highly desirable in an information society. Liquid crystalline photonic crystals (LCPCs) have been widely investigated in anti‐counterfeiting applications because of their intrinsic Bragg reflection and sensitive responsiveness to multiple external fields. However, current LCPC‐based anti‐counterfeiting methods suffer from sophisticated external fields, dopants, and limited color displays. Here, polychromatic anti‐counterfeiting is proposed using blue phase liquid crystal elastomer (BPLCE) films with only a uniform mechanical force. The elastic modulus can be tuned by controlling the crosslinking density via the ultroviolet (UV) exposure dosage. Therefore, by spatially designing the modulus distribution on a BPLCE film, color discrepancy occurs, and information carried by the modulus value emerges while the film is stretched. Bicolor and tricolor anti‐counterfeiting are presented for proof‐of‐concept, and the wavelength tuning range reaches 194 nm while the bandwidth remains as narrow as 25 nm with a custom high‐precision electrically driven biaxial displacement platform. This approach paves a new way to achieve high‐quality polychromatic anti‐counterfeiting and may promote the development of liquid crystalline elastomers in intelligent optical elements, information security devices, and smart wearable devices.