Nanodiamond/cellulose nanocrystals composite-based acoustic humidity sensor

This paper fabricated a high-performance nanodiamond (ND)/cellulose nanocrystal (CNC) composite-based acoustic humidity sensor. First, the effects of changes in both mass and viscosity of humidity-sensitive films on the resonance displacement, vibration modes, and impedance characteristics of the quartz crystal microbalance (QCM) were discussed using the finite element simulation software COMSOL Multiphysics. Then, the surface morphology and elemental composition of ND/CNC composites were characterized by TEM and EDS. Next, the humidity-sensing properties of ND/CNC composites, including response sensitivity, humidity hysteresis, dynamic characteristics, and stability, were tested at a relative humidity range from 11.3 % to 97.3 % RH combined with QCM transducers. In addition, the humidity-sensing performance of the QCM sensors with different ratios of composites was compared. The best ND/CNC-based QCM humidity sensors exhibited high sensitivity (54.1 Hz/%RH), low humidity hysteresis (3.2%RH), and fast response/recovery times. Then the adsorption process and sensitivity mechanism of water molecules on ND/CNC composites were analyzed using Langmuir isothermal adsorption model. Finally, the potential application of ND/CNC composite-based QCM humidity sensor was illustrated with respiration monitoring as an example.