Activating Bubble's Escape, Coalescence, and Departure under an Electric Field Effect

Area of Science:

• Fluid mechanics
• Microfluidics
• Electromechanical systems

Background:

• Bubble dynamics are crucial in various applications, including heat transfer and microfluidics.
• Controlling bubble behavior (escape, coalescence, departure) is essential for optimizing these processes.
• Existing methods for bubble manipulation can be limited in their reversibility and control.

Purpose of the Study:

• To investigate the use of electric fields to actively control bubble dynamics.
• To analyze the mechanisms of bubble escape, coalescence, and departure induced by electric fields.
• To compare the effectiveness of different alternating current (AC) waveforms in manipulating bubble behavior.

Main Methods:

• Utilized a simple electrowetting-on-dielectric device with a copper electrode wire.
• Applied AC electric fields to single and multiple bubbles in deionized water.
• Developed an electromechanical model to analyze wettability gradients and capillary forces.
• Tested sine, ramp, and square AC waveforms at 60 V amplitude and 2 Hz frequency.

Main Results:

• Electric field application induced continuous bubble escape via contact angle imbalance and wettability gradients.
• Square AC waveforms demonstrated the farthest bubble escape, followed by sine and ramp waves.
• Bubbles arranged in geometric patterns moved outward from a central electrode; linear arrangements led to coalescence.
• Bubble departure occurred by overcoming disjoining pressure or via buoyancy, depending on film thickness.

Conclusions:

• Electric fields offer an active and reversible method for controlling bubble dynamics, including escape, coalescence, and departure.
• The electrowetting-on-dielectric device provides a versatile platform for manipulating bubbles in fluid systems.
• Understanding these electrically induced dynamics can enhance efficiency in heat transfer and microfluidic applications.