A discrete phase hybrid continuum-atomistic model for electrokinetics in nanofluidics

Abstract

The ever-growing field of micro- and nanotechnology has a great deal of interest in simulating dynamic phenomena of multiscale systems. Hybrid approaches that produce a trade-off between accuracy and computational costs play a key role in this area. In this study, an improved hybrid continuum-atomistic model is proposed for the simulation of electroosmotic flows in nanochannels. The aqueous solvent phase is modeled by the continuum four-way coupled Navier-Stokes equations, while a Lagrangian approach is used for the ion transport. Different forces, including the drag, buoyancy, Brownian, electrostatic, and ion-ion/wall-ion collision, and torques, including the drag and collision, govern the motion of ion particles. The ion-ion/wall-ion collision is taken into account by a discrete phase model, and the electric field is derived by the Poisson-Boltzmann closure. Results of the model, such as the change in bulk velocity with surface electric charge density, are validated by several molecular dynamics simulations and experimental observations available in the literature. It is shown that the present hybrid model is capable of predicting the main features of the problem. Moreover, the significance of different forces and the other alternative for modeling the external electric field, i.e., the discrete Coulomb’s approach with the modified particle mesh Ewald boundary treatment, are also examined. The proposed model would be extremely useful for future studies on the electrokinetics in nanochannels, especially in more complex geometries where the molecular dynamics approaches are limited due to the computational costs.