Nonlinear amplification in electrokinetic pumping in nanochannels in the presence of hydrophobic interactions.

We discover a nonlinear coupling between the hydrophobicity of a charged substrate and electrokinetic pumping in narrow fluidic confinements. Our analyses demonstrate that the effective electrokinetic transport in nanochannels may get massively amplified over a regime of bare surface potentials and may subsequently get attenuated beyond a threshold surface charging condition because of a complex interplay between reduced hydrodynamic resistance on account of the spontaneous inception of a less dense interfacial phase and ionic transport within the electrical double layer. We also show that the essential physics delineated by our mesoscopic model, when expressed in terms of a simple mathematical formula, agrees remarkably with that portrayed by molecular dynamics simulations. The nontrivial characteristics of the initial increment followed by a decrement of the effective zeta potential with a bare surface potential may open up the realm of hitherto-unexplored operating regimes of electrohydrodynamically actuated nanofluidic devices.