Thèses

Jeudi 14 Octobre 2021 à 14h30.

Hydrodynamics and Energy Conversion in Nanofluidic Systems: A Molecular Perspective

''Nanofluidics, the study of fluid transport at nanometer scales, appears as a promising field to tackle some great challenges faced by our society, such as the development of alternative sustainable energies. Nanofluidic devices could contribute to energy conversion by e.g. the use of membranes with nanoscale porosity, which produce electricity from the different salt concentrations between fresh and seawater at the estuaries. Nanodevices could be also used to harvest waste heat by e.g. generating osmotic flows or electric currents from temperature gradients via thermo-osmosis or thermoelectricity. As the size decreases, surfaces have an increasingly important role, and it is critical at the nanoscale to understand the molecular mechanisms occurring at liquid-solid interfaces. One important property is the failure of the hydrodynamic no-slip boundary condition. Instead, a velocity jump occurs at the interface, defining the slip velocity, which is related to the liquid-solid friction coefficient. During my PhD, we focused in better understanding and characterizing the slip boundary condition, using classical molecular dynamics simulations. In particular, we studied the temperature dependence of the liquid-solid friction coefficient, and compared it to its bulk transport analogous, the shear viscosity of the fluid. With a special focus on supercooled water, we revealed the molecular mechanisms controlling friction by decomposing the interfacial transport coefficient into a static and a dynamic contribution, and we assessed the effect of supercooling on the large slippage we observed at the lower temperatures. Finally, we also studied thermo-osmosis flows, by proposing an analytical model that accounts for specific interactions between solvent and ions with the wall. Within this model, we studied the parameters that control the thermo-osmotic response of the system, predicting large responses for systems with large slippage, and a change of the osmotic flow direction with the salt concentration, which could explain experiments where the flow direction cannot be predicted by the classical theory

Directeur de thèse / thesis director: Laurent JOLY

Membres du jury / members of the jury:
Guillaume GALLIERO (Rapporteur)
Céline LEONARD (Rapporteure)
Catherine BARENTIN (Examinatrice)
Daan FRENKEL (Examinateur)
Aziz GHOUFI (Examinateur)
Virginie MARRY (Examinatrice)
Laurent JOLY (Directeur de thèse)
Samy MERABIA (Invité)


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