Massive amplification of surface-induced transport at superhydrophobic surfaces

Abstract

We study electro- and diffusio-osmosis of aqueous electrolytes at superhydrophobic surfaces by means of computer simulation and hydrodynamic theory. We demonstrate that the diffusio-osmotic flow at superhydrophobic surfaces can be amplified by more than 3 orders of magnitude relative to flow in channels with a zero interfacial slip. By contrast, little enhancement is observed at these surfaces for electro-osmotic flow. This amplification for diffusio-osmosis is due to the combined effects of enhanced slip and ion surface depletion or excess at the air-water interfaces on superhydrophobic surfaces. This effect is interpreted in terms of capillary driven Marangoni motion. A practical microfluidic pumping device is sketched on the basis of the slip-enhanced diffusio-osmosis at a superhydrophobic surface.