Electric field effect on the contact angle for non-wetting drops

Area of Science:

• Physics
• Materials Science
• Surface Science

Background:

• Electrowetting phenomena are critical in microfluidics and surface engineering.
• Existing models often simplify the complex interactions at the solid-liquid interface.
• Understanding the precise contact angle behavior under electrical fields is essential for device design.

Purpose of the Study:

• To develop a microscopic model for electrowetting of conducting drops on dielectric substrates.
• To derive an augmented Young-Laplace equation accounting for interatomic forces.
• To analyze contact angle behavior with and without applied voltage.

Main Methods:

• Formulation of a microscopic model including van der Waals and Born repulsive forces.
• Derivation of an augmented Young-Laplace equation.
• Calculation of wetting phenomena under varying electrical conditions.

Main Results:

• A well-defined Young's angle is established in the absence of an electric field, dependent on material properties.
• With an applied electric field, the meniscus angle transitions from near zero at the three-phase line (TPL).
• The Lippmann angle is only established at distances significantly beyond the dielectric thickness.

Conclusions:

• The initial contact angle near the TPL is not the Lippmann angle.
• Careful interpretation of apparent contact angle measurements is necessary.
• The model provides insights into the physics governing electrowetting dynamics.