Quantum friction in nanoscale fluid transport

The fluid flow in a macroscopic channel is typically determined assuming no-slip boundary conditions at the walls. Such an assumption no longer holds for nanoscale flow, and the finite flow slippage at the walls is a crucial determinant of a channel’s permeability. However, there is to date no predictive theory of the solid-liquid friction coefficient. Indeed, existing models rely on the idea of surface roughness, which is no longer relevant for atomically smooth surfaces that occur in nanofluidic devices. Particularly, one has to account for the presence of conduction electrons on the surface, which at the relevant length and time scales require the framework of many-body quantum mechanics.
We have developed a non-equilibrium field theory formalism that consistently describes the dynamics of a fluid coupled to surface conduction electrons. This description reveals a new contribution to solid-liquid friction, which results from electronic excitations in the solid, namely plasmons and electron-hole pairs. As such, we show that fluid flow at the nanoscale is impacted by intrinsically quantum properties of the confining material. Our results are of particular relevance to the water-carbon system, and provide an explanation for the peculiar slippage behavior of carbon nanotubes.