Triboelectrification between smooth metal surfaces coated with self-assembled monolayers (SAMs)

Area of Science:

• Surface Science
• Tribology
• Nanotechnology

Background:

• Triboelectrification, the generation of charge through contact and separation of surfaces, is a common phenomenon.
• Understanding the fundamental mechanisms of charge generation during friction is crucial for various applications, from electronics to material design.
• Molecularly smooth surfaces offer a unique platform to study friction and charge transfer at the nanoscale.

Purpose of the Study:

• To simultaneously measure friction and triboelectrification between similar and dissimilar molecularly smooth surfaces.
• To investigate the influence of load, friction, sliding history, and surface symmetry on triboelectrification.
• To elucidate the underlying mechanisms of charge generation during tribological processes.

Main Methods:

• Utilizing a modified surface forces apparatus for simultaneous friction and triboelectrification measurements.
• Employing hexadecanethiol-coated metal surfaces on mica substrates to create well-defined interfaces.
• Systematically varying parameters such as load, sliding distance, and surface combinations (similar vs. dissimilar).

Main Results:

• Dissimilar surfaces exhibited a dramatic increase in tribocurrent with increasing load, accompanied by significant fluctuations.
• Shearing similar surfaces resulted in no observable charge transfer or fluctuations.
• Triboelectrification was found to be sensitive to friction type (stick-slip vs. smooth), load, friction force, sliding distance, and prior surface history.

Conclusions:

• Frictional dissipation on dissimilar surfaces induces electron-hole formation and charge transfer.
• Molecular-level roughness, defects, and local dielectric constant variations play a key role in generating tribocurrents.
• The observed triboelectric effects are dependent on the asymmetry of the shearing surfaces and specific tribological conditions.