Preparation and performance evaluation of humidity-sensitive color-changing materials via hyperspectral imaging

Environmentally friendly humidity-sensitive color-changing materials have important applications in humidity indication. Two humidity-sensitive color-changing materials are prepared by utilizing bromocresol purple (BCP)/bromothymol blue (BTB) as humidity color-changing agents, boric acid as chromogenic agent and porous ceramic as substrate. To verify the repeatability and color-changing behavior of humidity-sensitive color-changing materials, a novel quantitative model of humidity is developed using hyperspectral imaging (HSI) and the K-nearest Neighbor (KNN) model. The two samples based on the KNN model can be achieved to match the measured values of ten humidity levels and show good repeatability after 35 cycles. The reflectance of two samples rapidly changed and stabilized within four minutes at a fixed humidity, which reflects their high humidity sensitivity . The predicted values of BCP sample based on KNN model are closer to the measured values of humidity levels in the range of 85–100% RH, while the predicted values of BTB sample based on KNN model are closer to the measured values of humidity levels in 7%− 23% and 85%− 100% RH range . Visualized assessment of humidity levels at each pixel can be obtained to provide a new approach to real-time monitoring of humidity changes , which shows potential applications in many areas.