la6b03640_si_001.pdf (1.09 MB)
Detection of Liquid Penetration of a Micropillar Surface Using the Quartz Crystal Microbalance
journal contribution
posted on 2016-12-14, 00:00 authored by Pengtao Wang, Junwei Su, Mengyan Shen, Marina Ruths, Hongwei SunA quantitative characterization
of the wetting states of droplets
on hydrophobic textured surfaces requires direct measurement of the
liquid penetration into surface cavities, which is challenging. Here,
the use of quartz crystal microbalance (QCM) technology is reported
for the characterization of the liquid penetration depth on a micropillar-patterned
surface. The actual liquid–air interface of the droplet was
established by freezing the droplet and characterizing it using a
cryogenically focused ion beam/scanning electron microscope (cryo
FIB-SEM) technique. It was found that a direct correlation exists
between the liquid penetration depth and the responses of the QCM.
A very small frequency shift of the QCM (1.5%) was recorded when the
droplet was in the Cassie state, whereas a significant frequency shift
was observed when the wetting state changed to the Wenzel state (where
full liquid penetration occurs). Furthermore, a transition from the
Cassie to the Wenzel state can be captured by the QCM technique. An
acoustic–structure-interaction based numerical model was developed
to further understand the effect of penetration. The numerical model
was validated by experimentally measured responses of micropillar-patterned
QCMs. The results also show a nonlinear response of the QCM to the
increasing liquid penetration depth. This research provides a solid
foundation for utilizing QCM sensors for liquid penetration and surface
wettability characterization.