Fig. 42.

(a) Frequency shifts as a function of RH for QCM sensors coated with three different sensing structures. (b) Response and recovery characteristic curves (three cycles) of QCM-based PEI/PA-6 NFN sensors with RH cycling between 2% RH and 35% RH. (c) Humidity hysteresis characteristic of QCM-based PEI/PA-6 NFN sensor. The coating loads of PEI and PA-6 were 4000 and 1400 Hz, respectively. (d) Schematic illustration of the humidity sensing mechanism of QCM-based PEI/PA-6 NFN sensor. Reprinted with permission from [29]. © 2011 Royal Society of Chemistry.