Flows at Molecular Scales: Probing and Manipulating Ultra-Thin Supported Liquid Films

A hydrodynamical description of a liquid down to molecular levels has to take into account the effects specific to these very small scales. At molecular distances from a solid wall, phenomena such as slip or confinement-induced molecular layering have been observed with liquids in both experiments and numerical simulations. The ability to predict those effects is crucial in many fields involving flows at small scales close to a solid, such as nanofluidics or flows in mesoporous media. However, a unifying picture of the different reported features is still lacking, partly because their manifestations critically depend on the chemical nature of both the liquid and the solid medium.

We have developed a fully non invasive optical technique [Phys. Rev. Lett., 114, 227801 (2015)] in order to characterize the dynamics of a liquid by measuring the spontaneous thermal fluctuations of its free surface. Liquid films lying on solid substrates are formed with a thickness down to 5 nm using a Marangoni (surface tension gradient induced) flow. Using this technique, we evidence disjoining pressure effects, and are able to probe flow properties of ultra-thin liquid films.