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Inventions 2018, 3(3), 46; https://doi.org/10.3390/inventions3030046

Adjustment and Measurement of Contact Angle with Electrowetting on a Quartz-Crystal Microbalance

1
Institute of Nanotechnology, National Chiao Tung University, Hsinchu 30010, Taiwan
2
Department of Mechanical Engineering, National Taiwan University, Taipei 10617, Taiwan
*
Author to whom correspondence should be addressed.
Received: 4 June 2018 / Revised: 26 June 2018 / Accepted: 26 June 2018 / Published: 10 July 2018
(This article belongs to the Special Issue Microfluidics and Nanofluidics)
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Abstract

Electrowetting-on-dielectric (EWOD) has been widely exploited as an actuating force to manipulate liquids by surface tension and modulation of the contact angle on a microscale. To evaluate EWOD, an optical measurement of the droplet contact angle is conventional, but is constrained by the optical properties of the liquid, especially when two liquid phases (e.g., water in oil) are involved. We developed a non-optical method to study EWOD using a quartz-crystal microbalance (QCM). A QCM provides a promising technique for mass sensing, and has been developed for the study of liquid viscosity, density and contact angle. In this research, a QCM was employed to generate EWOD and concurrently to measure the variation of the contact angle. The contact angle of droplets of water in air and in oil was evaluated. The voltage-dependent oil film between a water droplet and the QCM surface was sensed. A modified QCM model considering a voltage-dependent oil film was derived for the analysis of the contact angle. View Full-Text
Keywords: electrowetting; contact angle; quartz-crystal microbalance electrowetting; contact angle; quartz-crystal microbalance
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Lin, J.-W.; Wang, D.-S.; Fan, S.-K. Adjustment and Measurement of Contact Angle with Electrowetting on a Quartz-Crystal Microbalance. Inventions 2018, 3, 46.

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