Electrokinetic flows and surface conductivity on plain and nanostructured surfaces

At very low ionic strengths below 1 mM, for which the electrical conductivity of the electrolyte solution is extremely small, so-called surface conductivity due to nontrivial interfacial phenomena becomes the dominant contribution to the micro/nanochannel electrical conductance. This effect is detrimental for many important applications of electrokinetic flows using micro/nanofluidic devices that operate with low electrolyte concentrations. This talk will present recent experimental and theoretical results on the effect that the nanoscale surface topography has on the electrical surface conductivity over a wide range of ionic strengths (0.01 to 10 mM) for aqueous solutions of 1:1 electrolytes in slit micro/nanochannels with hydrophilic and hydrophobic surfaces. The presented results provide new insights on the diverse electrokinetic phenomena (e.g., Stern layer and interfacial ion mobility) that controls the surface conductivity observed in slit micro/nanochannels, and propose simple strategies to control it or reduce it when desired.