Instability of electrokinetic microchannel flows with conductivity gradients

Lin, Hao; Storey, Brian D.; Oddy, Michael H.; Chen, Chuan‐Hua; Santiago, Juan G.

doi:10.1063/1.1710898

Cited by 226 publications

(274 citation statements)

References 27 publications

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“…High conductivity ratio is a critical parameter for the electrokinetic instabilities we have observed (Chen & Santiago 2002a;Lin et al 2004). In the current set-up, we visualized homogeneous flow cases with 1 : 1 conductivity ratio at 10 mm or 1 mm, and verified that both of these flow conditions were stable at all applied voltages (0-3 kV).…”

Section: Resultsmentioning

confidence: 99%

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Convective and absolute electrokinetic instability with conductivity gradients

et al. 2005

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Electrokinetic flow instabilities occur under high electric fields in the presence of electrical conductivity gradients. Such instabilities are a key factor limiting the robust performance of complex electrokinetic bio-analytical systems, but can also be exploited for rapid mixing and flow control for microscale devices. This paper reports a representative flow instability phenomenon studied using a microfluidic T-junction with a cross-section of 11 µm by 155 µm. In this system, aqueous electrolytes of 10:1 conductivity ratio were electrokinetically driven into a common mixing channel by a steady electric field. Convectively unstable waves were observed with a nominal threshold field of 0.5 kV cm −1 , and upstream propagating waves were observed at 1.5 kV cm −1 . A physical model has been developed for this instability which captures the coupling between electric and flow fields. A linear stability analysis was performed on the governing equations in the thin-layer limit, and Briggs-Bers criteria were applied to select physically unstable modes and determine the nature of instability. The model predicts both qualitative trends and quantitative features that agree very well with experimental data, and shows that conductivity gradients and their associated bulk charge accumulation are crucial for such instabilities. Comparison between theory and experiments suggests the convective role of electro-osmotic flow. Scaling analysis and numerical results show that the instability is governed by two key controlling parameters: the ratio of dynamic to dissipative forces which governs the onset of instability, and the ratio of electroviscous to electro-osmotic velocities which governs the convective versus absolute nature of instability.

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Section: Resultsmentioning

confidence: 99%

“…The spatial framework also helps in determining the nature of instability and unfolding the physics of the instability. See Lin et al (2004) for a temporal stability analysis and nonlinear simulation of a similar instability phenomenon.…”

Section: Introductionmentioning

confidence: 99%

Convective and absolute electrokinetic instability with conductivity gradients

et al. 2005

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“…The final term in the momentum equations represents the electric body force, which accounts for a force exerted on the fluid by regions of net free charge moving under the influence of an electric field. In our domain of interest, this net charge resides in the bulk liquid (outside the electric double layer) and is associated with the coupling of electric field and conductivity gradients (see Lin et al 2004 for further discussion). We assume constant permittivity and extract from the divergence operator.…”

Section: Governing Equations and Boundary Conditionsmentioning

confidence: 99%

“…All dispersion models have also neglected the effects of electrohydrodynamic body forces associated with the coupling of conductivity gradients and diffusion at ITP interfaces. Such coupling creates regions of net free charge in the bulk liquid (outside the electric double layer) that can modify electrokinetic flow and lead to instabilities (Lin et al 2004;Chen et al 2005;Sounart & Baygents 2007;Santos & Storey 2008;Persat & Santiago 2009).…”

Section: Introductionmentioning

confidence: 99%

Sample dispersion in isotachophoresis

Garcia-Schwarz¹,

Bercovici²,

Marshall³

et al. 2011

J. Fluid Mech.

115

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We present an analytical, numerical and experimental study of advective dispersion in isotachophoresis (ITP). We analyse the dynamics of the concentration field of a focused analyte in peak mode ITP. The analyte distribution is subject to electromigration, diffusion and advective dispersion. Advective dispersion results from strong internal pressure gradients caused by non-uniform electro-osmotic flow (EOF). Analyte dispersion strongly affects the sensitivity and resolution of ITP-based assays. We perform axisymmetric time-dependent numerical simulations of fluid flow, diffusion and electromigration. We find that analyte properties contribute greatly to dispersion in ITP. Analytes with mobility values near those of the trailing (TE) or leading electrolyte (LE) show greater penetration into the TE or LE, respectively. Local pressure gradients in the TE and LE then locally disperse these zones of analyte penetration. Based on these observations, we develop a one-dimensional analytical model of the focused sample zone. We treat the LE, TE and LE-TE interface regions separately and, in each, assume a local Taylor-Aris-type effective dispersion coefficient. We also performed well-controlled experiments in circular capillaries, which we use to validate our simulations and analytical model. Our model allows for fast and accurate prediction of the area-averaged sample distribution based on known parameters including species mobilities, EO mobility, applied current density and channel dimensions. This model elucidates the fundamental mechanisms underlying analyte advective dispersion in ITP and can be used to optimize detector placement in detection-based assays.

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“…Dielectric force can also contribute to the instabilities. However, one essential condition for the instabilities is that the electric field should be very high [18]. In this work, only low electric field situation is considered and we assume that instabilities will not occur.…”

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confidence: 99%

Effects of ionic concentration gradient on electroosmotic flow mixing in a microchannel

Peng

2015

Journal of Colloid and Interface Science

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Effects of ionic concentration gradient on electroosmotic flow (EOF) mixing of one stream of a high concentration electrolyte solution with a stream of a low concentration electrolyte solution in a micrichannel are investigated numerically. The concentration field, flow field and electric field are strongly coupled via concentration dependent zeta potential, dielectric constant and electric conductivity. The results show that the electric field and the flow velocity are nonuniform when the concentration dependence of these parameters is taken into consideration. It is also found that when the ionic concentration of the electrolyte solution is higher than 1M, the electrolyte solution essentially cannot enter the channel due to the extremely low electroosmotic flow mobility. The effects of the concentration dependence of zeta potential, dielectric constant and electric conductivity on electroosmotic flow mixing are studied.

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Instability of electrokinetic microchannel flows with conductivity gradients

Cited by 226 publications

References 27 publications

Convective and absolute electrokinetic instability with conductivity gradients

Convective and absolute electrokinetic instability with conductivity gradients

Sample dispersion in isotachophoresis

Effects of ionic concentration gradient on electroosmotic flow mixing in a microchannel

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