Complex effects in micro-scale and nano-scale electrokinetics: significance of computational modeling and overcoming its challenges

A. Mani, M.B. Andersen, C.L. Druzgalski, S. Alizadeh
Stanford University, US

Keywords: electrokinetic chaos, continuum modeling, large-scale computing, ion-selective surfaces

Summary:

Electrokinetic phenomena are often described by the Poisson-Nernst-Planck and Navier-Stokes equations. However, the mainstream models describing solutions to these equations are based on asymptotic simplifications including bulk electroneutrality, quasi-steadiness, and/or quasi-equilibrium. In this presentation we will demonstrate the need for the development of specialized algorithms for simulation of electrokinetic phenomena, similar to the tools that have been traditionally used for simulation of turbulent flows. At the core of our investigation we consider ion transport through an ion-selective surface as a model problem with applications in electrochemistry, water purification, electrolysis and lab-on-a-chip systems. We will present results from our research and show that direct calculations, without asymptotic simplifications, can predict electrokinetic chaos with multi-scale vortices consistent with recent experimental observations. These calculations require resolving a wide range of spatio-temporal scales using unsteady solvers and often need massively parallel computational resources. Similar to turbulence simulations and in contrast to the mainstream commercial software, non-dissipative numerical discretization is crucial for effective preservation of physics of chaotic vortices. We will discuss how development of such high-fidelity tools can lead to fundamental understanding of complex effects in electrokinetic systems and facilitate their design and optimization.