Friction as a probe of surface properties of a polymer glass

TL;DR

This study investigates how friction at a polymer-glass interface varies with temperature, revealing a nanometer-thick mobile layer and pinning dynamics driven by localized rotational motions, advancing understanding of surface interactions.

Contribution

It demonstrates the existence of a mobile surface layer on glassy polymers and links friction behavior to microscopic pinning and rotational dynamics at the interface.

Findings

Friction depends on temperature due to surface pinning effects.

A nanometer-thick mobile chain layer exists at the polymer surface.

Pinning dynamics are governed by localized rotational motions.

Abstract

We probe the temperature dependence of friction at the interface between a glassy poly(methylmethacrylate) lens and a flat substrate coated with a methyl-terminated self-assembled monolayer. The monolayer exhibits density defects which act as pinning sites for the polymer chains. We show that the shear response of such an interface supports the existence, at the surface of the glassy polymer, of a nanometer-thick layer of mobile chains. Friction can be ascribed to the interplay between viscouslike dissipation in this layer and depinning of chains adsorbed on the substrate. We further show that the pinning dynamics is controlled by \beta rotational motions localized at the interface.