Viscoelasticity-Induced Onset of Slip at the Wall for Polymer Fluids
Résumé
The role of the polymer volume fraction, φ, on steady state slippage and interfacial friction is investigated for a semi-dilute polystyrene solutions in diethyl phthalate in contact with two solid surfaces. Significant slippage is evidenced for all samples, with slip lengths b obeying a power law dependence. The Navier's interfacial friction coefficient, k, is deduced from the slip length measurements and from independent measurements of the solutions viscosity η. The observed scaling of k versus φ clearly excludes a molecular mechanism of friction based on the existence of a depletion layer. Instead, we show that the data of η(φ) and k(φ) are understood when taking into account the dependence of the solvent friction on φ. 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.
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