At nanometric scales, surface effects obviously become predominant. Wall friction effects play a key role, impacting all transport processes - fluid, ionic, etc. They originate in molecular friction at the interface between the fluid, e.g. water, and the confining wall. These phenomena have been the subject of highly sophisticated experimental studies, involving a variety of specially developed tools which now enable us to study friction within single nanotubes or channels a few angstroms thick. We will discuss these results, particularly those in carbon nanotubes, which have provoked considerable debate in the literature.
In this lecture, we will then systematically introduce the theoretical framework for rationalizing interfacial friction phenomena, first in a classical and then in a quantum formalism. In particular, this will lead us to discuss the couplings that can emerge between classical water collective modes and quantum excitations within the confining material. This will lead us to discuss the consequences in terms of developing a " quantum engineering " of hydrodynamic flows. The effects of friction on transport will be discussed in relation to experimental results, particularly in the context of electrokinetic transport or mechano-sensitive effects.
