Challenges in using nano-textured surfaces to reduce pressure drop through microchannels

Advances in silicon processing and micro-machining now allow the consistent manufacture of micro- and nanoscale features necessary for the production of controlled roughness superhydrophobic surfaces. Superhydrophobic surfaces combine roughness features with low surface energy to create materials with substantially decreased wettability and, subsequently, reduced hydrodynamic drag. Thus, they represent a promising technology for reducing microchannel flow resistance; a major technical issue in microfluidic systems. In there, however, limits to the pressure a superhydrophobic surface can support before irreversible wetting transition occurs, leading to a loss of the drag-reducing effect. Of greater importance are preliminary observations that, even before a superhydrophobic surface wets irreversibly, the drag reduction over a superhydrophobic surface may be compromised by subtle changes in the three-phase contact line position. The positive impact of micro-geometries on heat transfer is well known. Coupling this phenomenon with superhydrophobic surfaces to reduce flow resistance, could represent a significant step forward in areas such as electronics cooling. However, theoretical models of superhydrophobic surfaces are complex due to the requirement for high resolution on multiple scales. This paper aims to present current results and discuss issues in implementing superhydrophobic surfaces, specifically nano-structured posts, in a microchannel.