Swelling characteristics and application of two-dimensional materials on hydrophilic quartz crystal resonant dew point sensor

The two-dimensional (2D) water adsorbing material is used as a sensitive layer for the hydrophilic quartz crystal resonant (QCR) dew point sensor, and its own swelling characteristics determine the accuracy of the sensor's recognition of the saturation status of the water vapor. In order to reveal the mechanism relationship between the swelling characteristics of materials and the measurement accuracy of hydrophilic QCR dew point sensors using different 2D materials, we used montmorillonite (MTT), graphene oxide (GO) and molybdenum disulfide (MoS2) coated QCR sensors to test dew point measurement performance in different humidity environment, and then the rate of swelling and intensity of swelling of the three materials were measured by integration of quartz crystal microbalance with dissipation (QCM-D) and ellipsometer. The results showed that MTT had an outstanding swelling rate and intensity with logrithmatic thickness changing curve, especially in the high humidity environment with sudden strength changes. This characteristic makes MTT the most suitable sensitive material for the hydrophilic QCR dew point sensor surface modification among the three 2D materials. Through this study, it implied that the rate of swelling and intensity of swelling are the two major parameters that determines whether a 2D material is suitable for being used as the sensitivity layer of a hydrophilic QCR dew point sensor.