8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Tue 611:23-14:00P9.21Efficiently accounting for ion correlations inelectrokinetic nanofluidic devices using densityfunctional theoryDirk Gillespie 11 Rush University Medical Center, 1750 W Harrison St, Suite 1289 IL, Chicago,United States of AmericaThe electrokinetic behavior of nanofluidic devices is dominated by the electrical double layers atthe device walls. Therefore, accurate, predictive models of double layers are essential for devicedesign and optimization. Density functional theory (DFT) of electrolytes (not electron orbitals) isan accurate and computationally efficient method for computing finite ion size effects and the resultingion-ion correlations. These include not only steric effects, but also electrostatic correlationsbeyond the mean field that produce nonlinear phenomena such as charge inversion, wherein morecounterions adsorb at the wall than is necessary to neutralize its surface charge, leading to a secondlayer of co-ions. The different dielectric coefficients of the electrolyte and the device wall canalso be included. DFT is shown to reproduce pressure-driven flow experiments exhibiting chargeinversion. Moreover, DFT predicts that charge inversion and other nonlinear phenomena lead toqualitatively different current densities and ion velocities for pressure-driven and electro-osmoticflows. Because DFT computes in 2-3 minutes for ion current in the nanoslit geometry, it is possibleto scan a large parameter space (e. g. , ion size, valence, concentration, slit height, wall surfacecharge) to understand how ion correlations produce novel current properties. Such characterizationis used to probe the theoretical limits of pressure-to-voltage power conversion and to probe whatdevice and electrolyte properties lead to efficient molecular recognition.21