Effect of the polystyrene surface hydrophobicity on QCM sensor resonance frequency in contact with water-glycerol mixture

Quartz Crystal Microbalance sensor responds to the mass change on the sensor surface as well as liquid viscosity and density which is in contact with the sensor surface. When the sensor surface was contacted with a liquid, the resonance frequency will decrease together with an increase of the series impedance of the sensor. Higher viscosity and density resulted in a decreased of the resonance frequency and increased the minimum impedance of the sensor. This paper showed that the surface hydrophobicity of the sensor surface also affected the change of the sensor resonance frequency as well as the sensor impedance. Surface hydrophobicity of the polystyrene coating was altered using UV irradiation. A variation of liquid viscosity was prepared by mixing water and glycerol. By varying the liquid viscosity from 1 to 2.6 cPs, the frequency and impedance change of the sensor was linearly related to the liquid viscosity. It was also observed that frequency and impedance change was also increase caused by a more hydrophilic surface. This result showed that lowering the hydrophobicity of the surface results in a better coupling between the sensor and the liquid. Those resulted in a higher energy transfer from the sensor to the liquid occurred and increased the sensor impedance.