Oscillating Electric Fields in Liquids Create a Long-Range Steady Field

Abstract

We demonstrate that application of an oscillatory electric field to a liquid yields a long-range steady field, provided the ions present have unequal mobilities. The main physics are illustrated by a two-ion harmonic oscillator, yielding an asymmetric rectified field whose time average scales as the square of the applied field strength. Computations of the fully nonlinear electrokinetic model corroborate the two-ion model and further demonstrate that steady fields extend over large distances between two electrodes. Experimental measurements of the levitation height of micron-scale colloids versus applied frequency accord with the numerical predictions. The heretofore unsuspected existence of a long-range steady field helps explain several longstanding questions regarding the behavior of particles and electrically-induced fluid flows in response to oscillatory potentials.

Charging Dynamics of Overlapping Double Layers in a Cylindrical Nanopore

“…Our results are also informative for ion transport inside nanopores for biosensing and nanofluidic applications [38,39], and are especially relevant for ion transport in conical nanopores [40]. Our approach can be extended to account for finite ion size [41], dielectric decrement [42], electrolyte valence [43,44], electrolyte mixtures [45], asymmetric diffusivities [46] and atomistic physics [47,48]. Finally, our approach can also be extended to ion-selective electrodes and large potentials where additional effects such as concentration polarization can become important [49].…”

Ions in an AC Electric Field: Strong Long-Range Repulsion between Oppositely Charged Surfaces

“…Manifold electrokinetic phenomena, such as electrohydrodynamic colloid manipulation [1,2], AC pumping [3], AC electro-osmosis (ACEO) [4], induced-charge electro-osmosis (ICEO) [5], induced-charge electrophoresis (ICEP) [6] and asymmetric rectied electric eld (AREF) [7] have been studied experimentally and theoretically [8,9]. To describe some of these phenomena classical models, like the Poisson-Boltzmann equation, have been modied and expanded, resulting in additional terms to account for large voltages [10,11], nite sizes of ions [12] and molecular crowding [13], and allows understanding many problems qualitatively and quantitatively.…”

“…[25]). On the contrary, for case of the capacitor lled with an electrolyte solution, a dierent behavior was observed: immediately after the application of the AC voltage, the surfaces were electrostatically attracted to each other as the result of a non-vanishing electric eld E -similar to [7] -and after approximately 30 seconds strong repulsion appeared ( We have developed a simplied model to describe the measured repulsion. For this purpose, we identied four distinct length scales present in the experiment of which three are known prior to experiment: the radius of curvature of the surfaces a = 2 cm, the separation between the surfaces H and the Debye length…”

Dynamic double layer force between charged surfaces

“…For nonplanar electrodes, one also has to account for the fluid flow and a hydrodynamic pressure along with the osmotic pressure considered here. Recent work regarding rectified electric fields in asymmetric electrolytes under an oscillatory voltage [42] suggests higher order contributions to the force beyond the limit of weak voltages considered here. That is, beyond the weak-voltage limit the frequency response will contain a host of higher harmonics in addition to the zeroth and second mode we consider.…”