Detection of liquid penetration of a micropillar surface using the quartz crystal microbalance

Pengtao Wang, Junwei Su, Mengyan Shen, Marina Ruths, Hongwei Sun

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

A 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.

Original languageEnglish
Pages (from-to)638-644
Number of pages7
JournalLangmuir
Volume33
Issue number2
DOIs
StatePublished - Jan 17 2017
Externally publishedYes

Funding

This work was supported in part by the National Science Foundation under grants CMMI 1031111 and CMMI 0923403. The authors thank Dr. George Cernigliaro and Dr. Wen Dai from MicroChem Corp. (Newton, MA) for their help in fabricating PMMA micropillars. The authors thank Mr. Christopher Santeufemio from the Materials Characterization Laboratory at University of Massachusetts Lowell for help with the cryo FIB-SEM.

FundersFunder number
National Science FoundationCMMI 0923403, CMMI 1031111

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