Interfacial charge density and its connection to adhesion and frictional forces

TL;DR

This paper establishes a theoretical link between electronic charge redistribution at solid interfaces and their adhesion and frictional properties, proposing new ways to measure and control friction through electronic means.

Contribution

It introduces a figure of merit for interfacial charge redistribution and demonstrates its applicability across various types of bonding, offering novel insights into friction control.

Findings

Charge redistribution governs adhesion and friction.

Functional relations hold for metallic, covalent, and physical bonds.

Inhibiting charge flow reduces adhesive friction, as shown with lubricant additives.

Abstract

We derive a connection between the intrinsic tribological properties and the electronic properties of a solid interface. In particular, we show that the adhesion and frictional forces are dictated by the electronic charge redistribution occurring due to the relative displacements of the two surfaces in contact. We define a figure of merit to quantify such charge redistribution and show that simple functional relations hold for a wide series of interactions including metallic, covalent and physical bonds. This suggests unconventional ways of measuring friction by recording the evolution of the interfacial electronic charge during sliding. Finally, we explain that the key mechanism to reduce adhesive friction is to inhibit the charge flow at the interface and provide examples of this mechanism in common lubricant additives.