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Dynamic contact angles and hysteresis under electrowetting-on-dielectric
Wyatt C Nelson1, Prosenjit Sen, Chang-Jin C J Kim
1Mechanical and Aerospace Engineering Department, University of California, Los Angeles, Los Angeles, California 90095, United States. wyattnelson@ucla.edu
Langmuir : the ACS Journal of Surfaces and Colloids
|July 15, 2011
Summary
This study measured dynamic contact angles and hysteresis using electrowetting-on-dielectric (EWOD). Hysteresis increases with EWOD voltage and sliding speed at high values, with stick-slip oscillations observed.
Area of Science:
- Fluid Dynamics
- Surface Science
- Materials Science
Background:
- Understanding droplet dynamics is crucial for microfluidics and surface engineering.
- Contact angle hysteresis influences droplet behavior and transport.
- Electrowetting-on-dielectric (EWOD) offers tunable control over droplet interfaces.
Purpose of the Study:
- To experimentally measure dynamic contact angles and hysteresis under EWOD.
- To investigate the influence of EWOD voltage and sliding speed on droplet dynamics.
- To evaluate the applicability of hydrodynamic and molecular-kinetic models.
Main Methods:
- Developed a novel experimental method for dynamic contact angle measurements.
- Conducted measurements across a range of electrowetting numbers (Ew) and capillary numbers (Ca).
- Applied Cox-Voinov and molecular-kinetic theory (MKT) models for data interpretation.
Main Results:
- Dynamic contact angle hysteresis is largely unaffected by EWOD voltage or sliding speed at low Ew or Ca.
- Hysteresis increases with both EWOD voltage and sliding speed at high Ew and Ca.
- Stick-slip oscillations were observed at Ew > 0.4; MKT provided reasonable fitting parameters.
Conclusions:
- EWOD significantly influences dynamic contact angle hysteresis at high voltage and speed.
- Existing models partially capture the observed phenomena, indicating a need for more complex theoretical frameworks.
- The study provides valuable data for understanding and predicting droplet behavior in EWOD systems.
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