Lubricated friction of textured soft substrates

TL;DR

This paper develops a universal, physics-based framework to understand and predict the lubricated friction of textured soft substrates, accounting for solid deformation and fluid flow, with implications for designing soft tribological systems.

Contribution

It introduces a model combining Reynolds' equations and elastic deformation to predict friction, revealing a universal scaling law for textured soft interfaces.

Findings

Friction exhibits a critical transition influenced by pattern geometry and material elasticity.

The model accurately predicts friction behavior across diverse soft materials and textures.

Friction scaling depends universally on elastic modulus and pattern geometry, independent of fitting parameters.

Abstract

The understanding of sliding friction for wet, patterned surfaces from first principles is challenging. While emerging applications have sought design principles from biology, a general framework is lacking because soft interfaces experience a multiphysics coupling between solid deformation and fluid dissipation. We investigate the elastohydrodynamic sliding of >50 patterned sliding pairs comprising elastomers, thermosets, and hydrogels, and discover that texturing induces a critical transition in the macroscopic friction coefficient. This critical friction scales universally, without any fitting parameters, with the reduced elastic modulus and the pattern geometry. To capture the frictional dissipation, we separate the flow curve into two regimes and account for the contributions of shear and normal forces applied by the fluid on the patterns. Our model combines Reynolds' equations and elastic deformation to provide physical insights that allow engineering of the elastohydrodynamic friction in a class of soft tribopairs using pattern geometry, material elasticity, and fluid properties.