Slip and friction mechanisms at polymer semi-dilute solutions / solid interfaces

TL;DR

This study investigates how polymer concentration affects slip and interfacial friction at polymer-solid interfaces, revealing that friction depends on solvent friction and is a semi-local phenomenon, challenging depletion layer models.

Contribution

It demonstrates that interfacial friction in semi-dilute polymer solutions depends on solvent friction and is not governed by depletion layers, supported by models of blob or monomer friction.

Findings

Slip length follows a power law with polymer concentration.

Interfacial friction coefficient scales with polymer volume fraction.

Friction is explained by solvent friction dependence, not depletion layers.

Abstract

The role of the polymer volume fraction, $\phi$, on steady state slippage and interfacial friction is investigated for a semi-dilute polystyrene solutions in diethyl phthalate in contact with two solid surfaces. Signicant slippage is evidenced for all samples, with slip lengths b obeying a power law dependence. The Navier's interfacial friction coecient, k, is deduced from the slip length measurements and from independent measurements of the solutions viscosity $\eta$. The observed scaling of k versus $\phi$ clearly excludes a molecular mechanism of friction based on the existence of a depletion layer. Instead, we show that the data of $\eta$($\phi$) and k($\phi$) are understood when taking into account the dependence of the solvent friction on $\phi$. Two models, based on the friction of blobs or of monomers on the solid surface, well describe our data. Both points out that the Navier's interfacial friction is a semi-local phenomenon.