Marceau Henot (ENS Lyon) - Slip of liquid polymers and morphogenesis of glacier tables

In this talk, I will first present a part of my PhD work on the slip of polymeric liquids. If this slip effect of a simple liquid on a solid surface is usually neglectable, it is not always the case for polymeric liquids. Using a method of velocimetry based on the observation under shear of a pattern photobleached in a fluorescent fluid, we systematically measured the slip length of polymeric liquids (PDMS) of various viscosities and at different temperatures on non-adsorbing surfaces in order to test the Navier hypothesis of a linear response at the interface. Comparing these measurements to friction experiments of PDMS elastomers on the same surfaces allowed us to discuss the hypothesis made by de Gennes in 1979 that the friction is controlled at the monomer scale.

In a second part I will present the work I started during my postdoc on the morphogenesis of glacier tables. These structures consist of a rock supported by a column of ice. They form naturally on glaciers through melting due to differential ablation of the ice. We investigated their formation by reproducing them at a smaller scale in a controlled environment. Using cylindrical caps made of materials of various thermal conductivity, we observed either the formation of a table standing on an ice foot, or the sinking of the cap into the ice block. By developing a simple model, we showed that the differential ice ablation rate is controlled by the thermal conduction through the cap leading to a competition between two effects: a geometrical amplification of the heat flux and a heat flux reduction due to the higher temperature of the cap compared to the ice.