High humidity responsive cholesteric liquid crystal polymer film for anti-counterfeiting encryption applications

Cholesteric liquid crystal polymer network (CLCN) films exhibit broad application prospects in sensing, information encryption, and anti-counterfeiting due to their unique optical properties. However, traditional CLCN films suffer from a narrow tunable range of the central wavelength of the reflection band and low response sensitivity. This study designs a porous hydrogen-bonded CLCN film. By introducing hydrogen bonds, the film demonstrated hygroscopic properties after alkali treatment. Additionally, the removal of the non-reactive liquid crystal (LC) generates pores, which further enhances its moisture absorption ability and significantly expands the tunable range of the reflection band's central wavelength. The experimental results show that the prepared CLCN film can achieve a very large adjustable range of 303 nm at the center wavelength of the reflection band under the condition of relative humidity (RH) of 40 %–90 %, and can achieve a fast response of 5s. Additionally, based on acid-base reversibility, two anti-counterfeiting methods were designed. One is a reversible, repeatable single-state anti-counterfeiting approach, while the other is an irreversible, one-time dual-state anti-counterfeiting method. In summary, through ingenious chemical design of CLCN films, this work optimized humidity-responsive properties and innovated information encryption technology. It not only provides new insights for designing stimulus-responsive polymer materials but also opens new avenues for advancing information security and anti-counterfeiting technologies.