Fluctuation-induced and quantum effects in nanofluidic transport
The hydrodynamic wall has traditionally been considered a featureless object, whose only role is to provide a boundary for fluid flow. Yet, there is now ample evidence that at nanometer scales, liquid flows are sensitive to the wall's internal -- in particular, electronic -- degrees of freedom. Here, after reviewing the experimental evidence for nanoscale liquid-electron couplings, we present the theoretical advances that have allowed for their quantitative understanding. We discuss how a quantum description of the liquid-solid interface reveals the influence of electron dynamics on classical fluid transport, in the form of the fluctuation-induced quantum friction effect. Quantum friction is at the root of liquid-electron coupled transport phenomena, that may be combined into a hydro-electronic transport matrix. We present analytical formulas for the hydro-electronic transport coefficients, that allow for their quantitative estimation in practical cases; we further outline the potential consequences of coupled liquid-electron transport for the water-energy nexus. Fluctuation-induced and quantum effects at liquid-solid interfaces represent an emerging interface between fluid dynamics and condensed-matter physics, and a largely uncharted territory for both theory and experiment.