Séminaire "Friction mechanisms of polymer solutions at solid/liquid interfaces" Frédéric Restagno (PHENIX)

Friction mechanisms of polymer solutions at solid/liquid interfaces

Séminaire de Frédéric Restagno (Univ. Paris-Saclay, Orsay)

le vendredi 13 décembre 2019 à 11h, salle des conseils de l’UFR de Chimie (32.42.101).

Résumé

Molecular friction mechanisms at solid-polymer interfaces is a key question in polymer rheology but also is of fundamental interest since it is a unique way to get access to the dynamics at the interface. The slippage of polymer melts is now well understood due to recent amazing experiments of dewetting, step leveling or by direct slip length measurements [1]. On ideal non-adsorbing surfaces, it was, in particular showed that the friction of polymer melt is due to the friction of monomers on the surface. We also showed that friction is a thermodynamically activated process, characterized by an energy of activation E_friction, different from the one of viscosity E_viscous. Depending on the sign of the difference between these energies, the slip length b can either increase or be constant [2].

The case of polymer solution is more complex since it involves both the competition between the solvent and the polymer. The friction mechanism on ideal non-adsorbing surfaces can be potentially affected by a depletion layer or can be due to the friction of the blobs sliding on the solid surfaces for semi-dilute solutions… There is indeed no clear picture of the mechanisms involved in this friction as measured by slip length measurements due to a lack of systematic measurements on controlled surfaces. We will review what is known for polymer friction at interfaces and present new slip length measurements of polystyrene in diethyl phthalate solutions on different surfaces. In particular, we will discuss if it is possible to extract a universal scaling law, for the slip length b with respect to the polymer concentration ɸ (see Figure).