Abstract
Induced-charge electroosmosis has attracted lots of attention from the microfluidic community over the past decade. Most previous researches on this subject focused on induced-charge electroosmosis (ICEO) vortex streaming actuated on ideally polarizable surfaces immersed in electrolyte solutions. Starting from this point, we conduct herein a linear asymptotic analysis on nonlinear electroosmotic flow next to leaky dielectric blocks of arbitrary electrical conductivity and dielectric permittivity in harmonic AC electric fields, and theoretically demonstrate that observable ICEO fluid motion can be generated at high field frequencies in the vicinity of nearly insulating semiconductors, a very low electrical conductivity, of which can evidently increase the double-layer relaxation frequency (inversely proportional to the solid permittivity) to be much higher than the typical reciprocal RC time constant for induced double-layer charging on ideally polarizable surfaces. A computational model is developed to study the feasibility of this high-frequency vortex flow field of ICEO for sample mixing in microfluidics, in which the usage of AC voltage signal at high field frequencies may be beneficial to suppress electrochemical reactions to some extent. The influence of various parameters for developing an efficient mixer is investigated, and an integrated arrangement of semiconductor block array is suggested for achieving a reliable mixing performance at relatively high sample fluxes. Our physical demonstration with high-frequency ICEO next to leaky dielectric blocks using a simple channel structure offers valuable insights into the design of high-throughput micromixers for a variety of lab-on-a-chip applications.
Highlights
Driven fluid streaming and particle transport are the eternal focus of electrokinetics, having undergone an exciting renaissance in micro/nanofluidics [1], electrochemistry [2] and functional biomedical devices [3,4] over the past ten years
Electroosmosis of conducting saline solutions in microchannels under an electric field externally applied across the channel length direction is generally dictated by the authoritative Helmholtz–Smoluchowski slip equation, which is obtained by dealing with the electric double layer (EDL) as a thin capacitor skin covered at a sharp material interface between the liquid and solid material of a native surface charge layer (Please refer to Ref. [5] for recent theoretical descriptions of triple charge layers near conducting media, including an ultrathin surface charge layer of free and bond charges, Debye screening cloud of counterionic charges, and an extended space charge region in desalinated regions): uEO
An investigation on induced-charge electroosmosis (ICEO) vortex streaming next to a leaky dielectric block lays the theoretical foundation for developing high-field-frequency electroosmosis micromixers
Summary
Driven fluid streaming (electroosmosis) and particle transport (electrophoresis) are the eternal focus of electrokinetics, having undergone an exciting renaissance in micro/nanofluidics [1], electrochemistry [2] and functional biomedical devices [3,4] over the past ten years. The polarized liquid layer near the phase interface is a sheet of electrical dipoles [7], and can be driven into electrophoretic motion by Coulomb force, giving rise to a distribution of velocity discontinuity at the sharp material interface between two distinct phases (Equation (1)) In this way, ‘force-free’ electrophoretic transport of freely suspended particles readily takes place in saline solutions of charge carriers, due to electroosmosis fluidic stress that are adjacent to the particle surface [7,8,9,10]: uEP
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