Effect of wetting states on frequency response of a micropillar-based quartz crystal microbalance

A new acoustic wave resonance device induced by coupling micropillars with a quartz crystal microbalance (QCM-P) was developed for potential use in a wide range of applications such as drug discovery and development. The effect of wetting states of liquid on the micropillars of the QCM-P devices becomes essential in understanding the frequency signals from QCM in these applications. Euler-Bernoulli beam theory-based models were developed to establish the relationship between the resonance frequency shift of QCM-P and different wetting states of liquid on the micropillar surface including Cassie and Wenzel states. To validate the models, micropillars were fabricated on a QCM substrate by using nanoimprinting lithography (NIL) and liquids with different viscosity and surface tension, as well as different surface treatments were utilized to achieve Cassie and Wenzel states. The experimental results show that both wetting states and micropillar height have profound impact on the frequency shift of the QCM devices and the model can accurately capture the resonance of the QCM-P device and predict the surface-liquid interactions with a reasonable accuracy.