Electrokinetic Pumping And Energy Conversion At Nanoscales

Abstract

The integration of the coupling effects of intrinsic wettability and surface charge in a nanochannel can cause non-intuitive behavior in the electrokinetic energy conversion processes. We demonstrate that in a nanofluidic device the energy conversion efficiencies may get amplified with an increase in surface charge density, not perpetually, but only over a narrow regime of low surface charges, and may get significantly attenuated to reach a plateau beyond a threshold surface charging condition. This results from the complex interplay between fluid structuration and ionic transport within a charged interfacial layer. We explain the corresponding findings from our molecular dynamics simulations with the aid of a simple modified continuum based theory. We attribute our findings to the four-way integration of surface charge, interfacial slip, ionic transport, and the water molecule structuration. The consequent complex non-linear nature of the energy transfer characteristics may bear far-ranging scientific and technological implications towards design, synthesis and operation of nano-batteries which can supply power at scales of the range molecular dimensions.