Seminar : Frédéric Restagno (Univ. Paris-Saclay) – 09/04/2021 at 11am

Abstract

A viscous fluid flowing near a wall can dissipates energy through its viscosity or through slip at the wall due to the friction of the last layer of fluid on the solid surface. For simple fluids, the adhesion of the molecules at the wall is so large than the slip effect is completely negligible. For polymer, the slip can be huge and the slip length which is the distance where the velocity profile of a shear flow extrapolates to zero, in the solid can be millimetric.This has been first theoretically explained by de Gennes [1].

Using a velocimetry technique based on fluorescent photobleaching [2], we systematically measured the slip length of different PDMS polymeric liquids on a non-adsorbing surfaces. In this talk, we will show that polymer fluids are a unique tool to understand the molecular mechanisms of friction of fluids, in general. We will in particular compare the friction of the PDMS liquids to the elastomer PDMS. We will propose a model to understand the complex effect of the temperature on the slip length [3] and (depending on the time) discussion the onset of friction [4].

References

[1] P.-G. de Gennes, CR Acad Sc Paris 288B, 219 (1979)

[2] Hénot, M., Chennevière, A., Drockenmuller, E., Léger, L., & Restagno, F. (2017). Comparison of the slip of a PDMS melt on weakly adsorbing surfaces measured by a new photobleaching-based technique. Macromolecules, 50(14), 5592-5598.

[3] Hénot, M., Grzelka, M., Zhang, J., Mariot, S., Antoniuk, I., Drockenmuller, E., … & Restagno, F. (2018). Temperature-controlled slip of polymer melts on ideal substrates. Physical review letters, 121(17), 177802.

[4] Grzelka, M., Antoniuk, I., Drockenmuller, E., Chennevière, A., Léger, L., & Restagno, F. (2020). Viscoelasticity-Induced Onset of Slip at the Wall for Polymer Fluids. ACS Macro Letters, 9(7), 924-928.