Size scaling of static friction

Area of Science:

• Materials Science
• Tribology
• Computational Physics

Background:

• Sliding friction on soft lubricants exhibits stick-slip behavior.
• Static friction force per unit area decreases with increasing contact area, based on molecular dynamics (MD) simulations.
• The large-size behavior of stick-slip friction remains unclear, with potential implications for smooth sliding and reduced kinetic friction.

Purpose of the Study:

• To formulate a scaling law for static friction force in soft lubricants.
• To investigate the dependence of static friction on contact area.
• To determine the conditions under which stick-slip behavior might vanish at larger scales.

Main Methods:

• Development of a theoretical scaling law for static friction force.
• Utilizing molecular dynamics (MD) simulations to model soft lubricant sliding.
• Comparing simulation results with the proposed scaling law.

Main Results:

• A scaling law is formulated, predicting static friction decreases as f(m)+Δf/A(γ) with increasing contact area A (γ>0).
• The parameter f(m) controls the persistence of stick-slip at large sizes and can be determined from small-size simulations.
• MD simulations confirm the theoretical predictions and the scaling law.

Conclusions:

• Stick-slip friction in soft lubricants is predicted to decrease with increasing contact area.
• The phenomenon of stick-slip may vanish at larger scales, leading to smooth sliding.
• The study provides a method to evaluate critical parameters for large-scale friction behavior using smaller-scale simulations.