Rapid-Response Low Humidity Sensor Based on Ionic Ladder-Type Poly(Silsesquioxane)

Accurate low-humidity detection is vital for applications such as lithium battery manufacturing, heritage preservation, and microelectronic packaging, yet current sensors face low sensitivity, slow response, and poor stability from limited water adsorption and slow ion transport. To address these challenges, a series of ionic ladder-like polysilsesquioxane (QLPSQ-X, X = Cl, FSI, BF4, or TFSI) were synthesized via quaternization followed by anion exchange. The rigid LPSQ framework ensures structural integrity, and its ionic groups enable efficient ion transport, yielding sensors with excellent linearity over 5%–97% RH. Specifically, the QLPSQ-TFSI sensor demonstrated the best linearity (R2= 0.99) and sensitivity (|log Ra/%RH| = 0.030) at 100 Hz, ultrafast response/recovery times (0.1 s/0.9 s at 5%–33% RH, 0.1/2.1 s at 5%–97% RH), low hysteresis (<12% RH), and stable operation (over 30 days). These superior properties arise from the optimized hydrophobicity, enhanced ion mobility, and the mesoporous LPSQ framework, enabling efficient low-humidity sensing.