Elastic Deformation of Soft Coatings Due to Lubrication Forces

TL;DR

This paper models how elastic deformation of soft coatings affects lubrication forces and fluid drainage between surfaces, providing new formulas and maps for better interpretation of experimental measurements.

Contribution

It combines lubrication theory and elasticity to analyze fluid drainage over stratified coatings, offering a comprehensive model for various coating thicknesses and properties.

Findings

Derived a simple expression for contact position shift during force measurements.

Showed that contact mechanics corrections are not applicable to elastohydrodynamic deformation.

Provided contour maps for estimating elastic deformation in surface force experiments.

Abstract

Elastic deformation of rigid materials with soft coatings (stratified materials) due to lubrication forces can also alter the interpretation of dynamic surface forces measurements and prevent contact formation between approaching surfaces. Understanding the role of elastic deformation on the process of fluid drainage is necessary, and the case where one (or both) of the interacting materials consists of a rigid substrate with a soft coating is still limited. We combine lubrication theory and solid linear elasticity to describe the dynamic of fluid drainage past a compliant stratified boundary. The analysis presented covers the full range of coating thicknesses, from an elastic foundation to a half-space for an incomressible coating. We decouple the individual contributions of the coating thickness and material properties on the elastic deformation, hydrodynamic forces, and fluid film thickness. We obtain a simple expression for the shift in contact position during force measurements that is valid for many experimental conditions. We compare directly the effect of stratification on the out-of-contact deformation to the well-known effect of stratification on indentation. We show that corrections developed for stratification in contact mechanics are not applicable to elastohydrodynamic deformation. Finally, we provide generalized contour maps that can be employed directly to estimate the elastic deformation present in most dynamic surface force measurements.