"Computational Nanofluidics"

Narayana Aluru, University of Illinois at Urbana-Champaign

There is a growing interest in investigating transport and electrochemical phenomena in nanometer channels and pores because of the possibility of mimicking selective ion transport found in protein channels in cell membranes of living systems and because of the revolutionary advances that can be enabled in many other application areas such as sensing, single molecule detection, water purification, energy storage, etc.  Several experimental approaches such as the track etch method and the ion beam method have been used with increasing success in recent years to characterize the ionic transport through nanopores of varying diameters. However, fundamental questions regarding the effects of confinement and charge on diffusion and mobility of ions need to be resolved for better design of these nanochannel/nanopore based devices and to propose novel sensing mechanisms based on chemical functionalization. The traditional continuum theory typically used in the analysis of electrochemical phenomena in micro-fluidic channels cannot take into account the effects caused by the finite size of the ions and water and the water accessible volume of the nanopore. This requires atomic scale simulations (e.g. molecular dynamics simulations) where finite size of ions and water is explicitly treated. However, order of the time scales and the length scales possible in atomistic molecular dynamics (MD) simulations is far less than realistic design calculations. Further, it is known that in small diameter nanopores (~ 3nm and less), the wall partial charges and the polarization effects can influence the transport coefficients. These can be computed from Density functional theory (DFT) or by semiempirical methods. In this talk, I will present computational studies towards a molecular understanding of fluids and the development of multiscale methods bridging across length scales. A number of results will be presented showing the significance of confinement, surface charge density and partial charges on water and ion transport.