Mathematical Modeling of Induced-Charge Electrokinetics

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Bazant 0707641 The investigator develops timely new mathematical models for nonlinear "induced-charge" electrokinetic phenomena, where electro-osmotic flows or particle motions are driven by electric fields acting on induced double-layer charge at polarizable (metal or dielectric) surfaces. The investigator and his colleagues have worked for five years on a unified theory of such effects, as well as related experimental studies in microfluidics and colloids. In spite of a number of successes in predicting new types of flows, however, the existing theory fails to predict some crucial features of the experiments, such as flow reversal at high voltage and flow suppression at high concentration. The theory is based on the classical Poisson-Nernst-Planck equations, which are strictly valid only for "small" voltages (< 25 mV), but experiments typically involve much larger voltages (> 1 V), which condense counterions near the surface and violate the dilute solution approximation. The investigator builds a mathematical theory for this regime by modeling steric and correlation effects due to ion crowding, nonlinear permittivity and viscosity of the solvent, and Faradaic reactions. The theory is tested against experiments and applied to design new microfluidic devices. This work has fundamental relevance for nanotechnology and biotechnology. Induced-charge electro-osmosis (ICEO) is a recently identified nano-scale phenomenon with many applications in microfluidics and colloids. Because ICEO can be exploited to manipulate fluids and particles with battery voltages, it could enable revolutionary new portable or implantable biomedical devices, such as tiny drug infusion pumps and diagnostic labs-on-a-chip. The mathematical work of the investigator seeks to advance our understanding of ICEO flows, especially in biological liquids, by exploring consequences of molecular crowding on the dynamics of electrolytes near highly charged surfaces.