Molecular simulations of electroosmotic flows in rough nanochannels

Abstract

A highly efficient molecular dynamics algorithm for micro and nanoscale electrokinetic flows is developed. The long-range Coulomb interactions are calculated using the Particle–Particle Particle–Mesh (P 3M) approach. The Poisson equation for the electrostatic potential is solved in physical space using an iterative multi-grid technique. After validation, the method is used to study electroosmotic flow in nanochannels with regular or random roughness on the walls. The results show that roughness reduces the electroosmotic flow rate dramatically even though the roughness is very small compared to the channel width. The effect is much larger than for pressure driven flows because the driving force is localized near the walls where the charge distribution is high. Non-Newtonian behavior is also observed at much lower flow rates. Systematic investigation of the effect of surface charge density and random roughness will help to better understand the mechanism of electrokinetic transport in rough nanochannels and to design and optimize nanofluidic devices.