A flexible polyethyleneimine film sensor for high humidity monitoring

High-humidity environments are of great significance to ecology, industrial and agricultural production, and human health. However, the simultaneous realization of high sensitivity, low hysteresis, high resolution, and outstanding linear response in a single flexible humidity sensor, especially for measuring high relative humidity (RH) levels, remains a great challenge. In this study, a flexible self-supporting sensing film capable of accurately detecting high moisture levels was fabricated by utilizing vinyl-functionalized polyethyleneimine as the humidity sensing material, eliminating the need for an additional flexible substrate. The as-prepared flexible self-supporting polyethyleneimine sensor demonstrated high sensitivity (1644%/%RH), minimal humidity hysteresis (0.6% RH), and excellent linearity (R2 = 0.9998) within the humidity range of 70% to 97% RH. Notably, the sensor boasted a high resolution of 0.1% RH with a strong linear response (R2 = 0.9846), enabling the real-time monitoring of human respiratory rates, speech patterns, and skin humidity variations. This work provides an innovative approach to constructing a polyethyleneimine humidity sensor for precise humidity measurement in high RH environments.