Asymmetrical Electrowetting on Dielectrics Induced by Charge Transfer through an Oil/Water Interface

Area of Science:

• Microfluidics
• Surface Science
• Electrochemistry

Background:

• Electrowetting on dielectrics (EWOD) is crucial for microfluid manipulation but faces challenges like contact angle saturation.
• Charge trapping on dielectric surfaces is a suspected cause of EWOD saturation, limiting device applications.
• Oil lubrication layers have shown promise in reducing EWOD contact angle saturation.

Purpose of the Study:

• To investigate the influence of an oil layer containing a dissolved dye on electrowetting behavior.
• To analyze the asymmetric electrowetting phenomenon observed with oil-lubricated hydrophobic surfaces.
• To elucidate the charge transfer mechanisms occurring at the oil/water interface during EWOD.

Main Methods:

• Monitoring water contact angles on oil-lubricated hydrophobic insulators with varying pH.
• Electrochemical analysis using cyclic voltammetry and thin-layer cyclic voltammetry.
• Measuring transient currents in dye-doped oil to identify charge carriers.

Main Results:

• An asymmetric electrowetting curve was observed on the oil-lubricated hydrophobic surface.
• Cyclic voltammetry confirmed redox reactions of the dye and potential decomposition.
• Ion transport across the oil/water interface and increased oil phase conductivity with dye concentration were confirmed.
• Transient current measurements suggested inverse micelle formation as a charge transport mechanism.

Conclusions:

• The study demonstrates an oil-property-dependent asymmetry in electrowetting.
• Charge transfer through the oil/water interface, facilitated by dye-induced mechanisms, is responsible for the observed asymmetry.
• This finding provides a novel understanding of EWOD behavior and potential mitigation strategies for saturation effects.