It is Separation, Not Contact: Electrification at Water-Hydrophobe Interfaces during Wetting-Dewetting Cycles

Area of Science:

• Physical Chemistry
• Surface Science
• Fluid Dynamics

Background:

• Interfacial electrification occurs when water contacts hydrophobic materials.
• The role of dynamic wetting and dewetting in this process is not well understood.

Purpose of the Study:

• To investigate the mechanisms governing electrification at water-hydrophobe interfaces during dynamic wetting and dewetting.
• To determine the key parameters controlling charge transfer at these interfaces.

Main Methods:

• Controlled pipetting experiments using hydrophobic capillaries.
• Systematic variation of liquid uptake and release rates over three orders of magnitude.
• High-resolution charge measurements.

Main Results:

• Electrification is governed by liquid-solid separation, not contact formation.
• Charge transfer depends nonlinearly on the velocity and acceleration of the receding meniscus.
• Charge generated during liquid release influences subsequent liquid uptake, indicating intercycle coupling.

Conclusions:

• Liquid-solid separation kinetics are the dominant control parameter for water-hydrophobe electrification.
• Interfacial charging is inherently history-dependent, with charge conservation best described across successive cycles.
• Findings advance understanding of interfacial charging and have implications for microfluidics and droplet technologies.