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TECHNICAL PAPERS

Reversible Electrowetting of Liquid-Metal Droplet

[+] Author and Article Information
Zhiliang Wan1

Department of Electrical and Computer Engineering,  University of Illinois at Chicago, 851 South Morgan St., Chicago, IL 60607zlwan@ece.uic.edu

Hongjun Zeng

Department of Electrical and Computer Engineering,  University of Illinois at Chicago, 851 South Morgan St., Chicago, IL 60607hzeng@ece.uic.edu

Alan Feinerman

Department of Electrical and Computer Engineering,  University of Illinois at Chicago, 851 South Morgan St., Chicago, IL 60607feinerman@uic.edu

1

Corresponding author.

J. Fluids Eng 129(4), 388-394 (Jun 02, 2006) (7 pages) doi:10.1115/1.2436582 History: Received April 06, 2006; Revised June 02, 2006

This paper reports experimental investigations on the electrowetting effect of liquid metals, e.g., mercury, on dielectric films. Largest contact angle change of 74deg (from 141degto67deg) is achieved on top of a Parylene film. Highly reversible electrowetting with very low hysteresis (24deg) is demonstrated on the Teflon®-coated surfaces. The actuation voltage for 30deg contact angle change (from 148degto118deg) is largely reduced to 25V by using a high-dielectric-constant tantalum oxide film as the dielectric layer. The effect of trapped charges in the dielectric film on the electrowetting is observed and measured. The rise and fall times of the electrowetting actuation are inversely proportional to the droplet diameter and as short as 0.10.2ms for a 50μmdia droplet. The actuation reliability is tested, and a long-time operation is achieved in an oil environment.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic sketches of electrowetting experimental setups: (a) with a fine metal probe and (b) with an on-plane electrode

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Figure 2

Diameter of the droplet jetted by Jetlab system as a function of the number of dispenses

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Figure 3

Electrowetting of a mercury droplet on a parylene film: the squares are measured contact angles and the solid line is a calculation based on Eq. 1. The inset shows the stills of the droplet at 0V and 180V.

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Figure 6

Shifting of electrowetting curve due to the charges trapped in the insulating film in the electrowetting experiment.

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Figure 7

Voltage step-response of electrowetting actuation on a Teflon AF-coated parylene film: evolution of the contact line length with time

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Figure 8

Electrowetting actuation of droplet driven by a 100Hz, 100V square voltage pulse: The evolutions of the contact angle (solid squares) and droplet height (open squares)

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Figure 9

Oscillation frequency of a bound liquid droplet as a function of the diameter

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Figure 10

Decaying of electrowetting actuation amplitude with time: (a) contact angle and (b) droplet base diameter

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Figure 4

Trajectory electrowetting measurements: (a) on a parylene surface, (b) on a vacuum-oil impregnated surface, and (c) on a Teflon AF-coated surface

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Figure 5

Electrowetting actuation voltage for achieving 30deg contact-angle change on dielectric films with different thickness and different dielectric constant (squares, parylene; triangle, silicon nitride; circle, tantalum oxide).

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