Improve the Dew Point Recognition Accuracy of QCM Dew Point Sensor via Electrode Surface Hydrophobic Treatment

In the quartz crystal microbalance (QCM)-based dew point (DP) measurement with active temperature control, water molecules in gas condense on the electrode surface. The formation of water microdroplets leads to a considerable decrease in the frequency response of QCM sensor. In addition to the frequency shift due to the mass change induced by condensation, we found that the viscous behavior of liquid water also leads to a dissipation, which limits the accuracy of DP recognition in air. Here, we proposed a QCM structure where a hydrophobic film is coated on electrode surface as an isolation layer to minimize the impact of water viscoelasticity. A series of silver electrode surfaces were prepared by hydrophobic treatment, and the modified electrode with a static contact angle of 134°±2° is applied in the DP measurement system to compare its performance with the untreated electrode. Taking the precision chilled-mirror hygrometer MICHELL S4000 as a standard, the experiments verified that the frequency dissipation attributed to the viscoelastic effect is reduced in the sensor with hydrophobic electrode. The proposed QCM with hydrophobic treatment can effectively improve the accuracy of DP recognition and further provide the theoretical and experimental basis for the optimal design of DP sensor.