Sliding friction between an elastomer network and a grafted polymer layer: the role of cooperative effects

TL;DR

This paper investigates how interactions among densely grafted polymer chains influence friction with elastomers, developing a model that predicts a saturation point in friction increase, aligning well with experimental observations.

Contribution

The study introduces a model accounting for cooperative effects among grafted chains, revealing a maximum grafting density where friction ceases to grow.

Findings

Friction force saturates at high grafting densities.

Interactions among grafted chains significantly affect friction.

Model predictions agree with experimental data.

Abstract

We study the friction between a flat solid surface where polymer chains have been end-grafted and a cross-linked elastomer at low sliding velocity. The contribution of isolated grafted chains' penetration in the sliding elastomer has been early identified as a weakly velocity dependent pull-out force. Recent experiments have shown that the interactions between the grafted chains at high grafting density modify the friction force by grafted chain. We develop here a simple model that takes into account those interactions and gives a limit grafting density beyond which the friction no longer increases with the grafting density, in good agreement with the experimental data