Liquid polymers are by far the most used material in our daily life and take a rich variety of forms. For instance, microgels in hair gels provide desire rheological response; polymer are used as food thickener;  long chain of polymers are used in motor oils for lubrication. Despite their omnipresence, understanding their flow in flow situations of practical importance (e.g. 3D printing, coatings, oil recovery) have proven to be difficult, mainly because of their complex rheology, but also because of their properties at interfaces. In this seminar, I will use two examples borrowed from our everyday life  that illustrate the very rich phenomenology of polymer flows.

In the first part of this seminar, I will talk about an everyday-life-object that we all have on our desk: the scotch tape. Have you ever taped a poster on a wall, came back later, and witnessed its fall?  One may see the scotch tape as a viscoelastic fluid, slowly flowing. In contrast, when you tape the end of a piece of scotch tape to the edge of a table, you usually observe that the tape does not unroll under its own weight: in that case, one could see the adhesive as a visco-elastic solid. I will explain how I solved this paradox by investigating commercial adhesive tapes in controlled conditions.

In a second part, I will discuss another fundamental polymer flow situation that is essential in many processes: the spreading of a liquid on a surface. The spreading of a drop of polymer melts is not captured by classical hydrodynamic laws at the contact line because the shear stress diverges at the interface between the drop and the solid surface. I will show that the spreading of polymer melts can be rationalized by proposing a multiscale approach to properly bridge the different length scales involved in the problem: the macro- and micro- scopic spreading properties of polymer melts, from the millimetric size of a drop to the nanoscale liquid/substrate interaction.

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