Real-time visual humidity response films of interpenetrating polymer network based on cholesteric liquid crystal and poly (acrylic acid)

Humidity sensors play a critical role in diverse fields such as agricultural production, medical equipment, and weather forecasting. However, the majority of existing humidity sensors rely on batteries or are relatively costly to construct. In this study, a simple, efficient, and battery-free visual humidity sensor was developed by combining cholesteric liquid crystal (CLC) with acrylic acid (AA) and subsequently curing it to form an interpenetrating polymer network (IPN) film. The IPN film changes colour with relative humidity (RH). Moreover, it has been confirmed that the film exhibits excellent repeatability, and its performance remains relatively unaffected by temperature fluctuations. Additionally, the relationship between film thickness and response time is explored in this research. Through orthogonal experiments involving various proportions of CLC, the study also scrutinises the influence of each component on the humidity response performance of the IPN films. During the transition from 40% RH to 90% RH, IPN film sample 3 experienced a remarkable redshift of 123.05 nm in the reflected wavelength. As for sample 9, its humidity response demonstrated an outstanding linearity of 0.9986. Consequently, the experimental outcomes provide strong evidence that this IPN film exhibits superior humidity response capabilities and holds considerable promise for practical applications.