Directional flow induced by synchronized longitudinal and zeta-potential controlling AC-electrical fields

Area of Science:

• Microfluidics
• Surface Chemistry
• Electrical Engineering

Background:

• Electroosmotic flow (EOF) is crucial for microfluidic devices.
• Controlling EOF typically involves managing surface charge.
• Existing methods face challenges like electrolysis.

Purpose of the Study:

• To demonstrate a Field Effect Flow Control (FEFC) structure for microchannel fluid manipulation.
• To show induction of directional flow using synchronized gate and axial potentials.
• To analyze the system's time constants and predict maximum operating frequencies.

Main Methods:

• Implementing an electrode as a gate to locally alter surface charge and zeta potential.
• Utilizing synchronized switching of gate and axial potentials to induce directional EOF.
• Developing an equivalent electrical circuit model to analyze insulator charging dynamics and time constants.
• Expanding the traditional three-capacitor model to include buffer capacitance for improved accuracy.

Main Results:

• Directional EOF was successfully induced by synchronized potential switching.
• Gas formation due to electrolysis was suppressed at high switching frequencies.
• The magnitude and direction of EOF were effectively maintained.
• Analysis of the electrical circuit provided insights into charging dynamics and pH dependency.

Conclusions:

• FEFC offers a viable method for precise electroosmotic flow control in microchannels.
• Synchronized potential switching is effective in inducing directional flow and mitigating electrolysis.
• An expanded electrical model accurately describes the charging dynamics and limitations for high-frequency operation.