A Drop-on-Micropillars (DOM)-Based Acoustic Wave Viscometer for High Viscosity Liquid Measurement

High viscosity measurement is critical for applications such as food manufacturing, drug development, and biomedical diagnostics. Vibration-based viscosity measurement devices have become increasingly popular due to their portability, cost efficiency, and low sample consumption. However, they suffered drawbacks such as low sensitivity and high damping and noise levels when measuring high-viscosity liquids due to the increased hydrodynamic loading on the vibrating structures. In this work, a novel drop-on-micropillar (DOM) concept is developed to improve the sensitivity and reduce the damping of the vibrational viscometers for high viscosity measurement by taking advantage of a liquid drop on a micropillar array under non-wetting state—Cassie state. In the meantime, the unique resonance phenomena between micropillars and acoustic wave substrate ( $\mu $ PAW)—quartz crystal resonator (QCR) can significantly improve the sensitivity of the original acoustic wave device. The DOM concept was realized by fabricating polymethyl methacrylate (PMMA) micropillars on a QCR surface by thermal nanoimprinting lithography (T-NIL), and the pillar surface was then modified through a chemical vapor deposition (CVD) technique to yield a superhydrophobic micropillar surface. The resonance frequency shift and quality factor of the devices were measured for deionized water and aqueous glycerol solution with viscosity ranging from 3 to 91.4 cP. The results show that the DOM device can achieve the measurement of viscous liquids at a high sensitivity while maintaining the quality factor (energy dissipation) within an acceptable level.