Friction between Polymer Brushes

TL;DR

This paper models the interpenetration and static friction between polymer brushes, showing that at light loads, surfaces can slide without entanglement due to osmotic pressure, aligning with experimental data.

Contribution

It provides a theoretical framework for understanding friction in polymer brush systems, linking equilibrium equations to frictional behavior.

Findings

Interpenetration depends on contact conditions.

Friction force matches experimental measurements.

Sliding occurs at light loads due to osmotic pressure.

Abstract

By solving the equilibrium equations for a polymer in a neutral polymer brush, the degree of interpenetration of two polymer brushes in contact and near contact is calculated. These results are used to calculate values of the force of static friction in agreement with recent friction measurements for polymer brush lubricated surfaces. It is shown that at sufficiently light loads polymer brush coated surfaces can slide, with the load supported entirely by osmotic pressure, at a sufficiently large spatial separation so as to avoid entanglement, and hence static friction.