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Watching molecular transport at interfaces
Molecular-scale dynamics at interfaces play a key role in a variety of processes in soft matter, from wetting, tribology, down to confined flow in nanofluidic devices. However, direct access to these interfacial transport processes at the molecular scale has remained a distant experimental goal. In this seminar, I will present some recent efforts towards this aim.
Focusing first on polymer/surface interactions, I will show how state-of-the-art single-molecule and super-resolution microscopy techniques can be used to track the nanoscale dynamics of single fluorescently tagged PEG macromolecules in solution at solid surfaces and under hydrodynamic flow. Allowing for direct observation of molecular-scale interfacial dynamics under out-of-equilibrium conditions, our approach brings a new molecular vision of macromolecular friction and adsorbate/surface interaction at flowing solid/liquid interfaces.
Relying on solid-state fluorescent emitting defects, I will show how these super-resolution techniques can be extended to track the transport of single ions at solid/liquid interfaces, as well as under nanofluidic confinement.
Finally, going back to the macroscopic scale, I will discuss the peculiar question of liquid triboelectrification, whereby liquid droplets sliding on hydrophobic surfaces lead to surface charging. I will show how we can map the spatial distribution of surface-trapped ionic charge, from which we evidence a very large 2D ionic mobility, suggesting that ionic surface transport takes place through the diffusion of mobile hydrated ions sliding with ultra-low friction at the solid/air interface.