Amontonian friction induced by flexible surface features on microstructured silicon

Area of Science:

• Tribology
• Materials Science
• Surface Physics

Background:

• Amontons' law traditionally describes friction as linearly dependent on load and independent of contact area and velocity.
• Microstructured surfaces introduce complexities to friction behavior not fully captured by classical laws.
• Understanding friction at the microscale is crucial for designing advanced materials and devices.

Purpose of the Study:

• To investigate the validity of Amontons' law under varying conditions using microstructured surfaces.
• To explore the influence of particle size and sliding velocity on friction dynamics.
• To identify the energy dissipation mechanisms governing friction in microscale contacts.

Main Methods:

• Measured friction force as a function of applied load between a spherical silica particle and a silicon surface with microneedles.
• Varied silica particle size and sliding velocity to test Amontons' law predictions.
• Analyzed friction force oscillations and average friction force against applied load.

Main Results:

• Friction force oscillated with microneedle spacing for small particles, indicating microneedle bending and release.
• Average friction force showed a linear relationship with applied load, consistent with Amontons' law, for most conditions.
• A deviation from Amontons' law was observed for small particles at low velocities, attributed to a changing energy dissipation mechanism.

Conclusions:

• Amontons' law holds when the primary energy dissipation mechanism remains constant with applied load.
• Microscale surface topography significantly influences friction dynamics, leading to phenomena like microneedle-induced oscillations.
• The study highlights the limitations of Amontons' law and suggests the need for load-dependent energy dissipation models at the microscale.