Electrokinetics of the silica-solution interface: a flat plate streaming potential study

Scales, Peter J.; Grieser, Franz; Healy, Thomas W.; White, Lee R.; Chan, Derek Y. C.

doi:10.1021/la00039a037

Cited by 309 publications

(273 citation statements)

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“…For the theory results, normalized zeta potentials display a nearly linear variation as a function of pH with a slope of 6.5 mV=pH (for pH > 7), comparable to the experimental value of 4-7 mV=pH [106]. Hence, our model can provide a rather good explanation of the measured zeta potential results, which have also been addressed by previous models with varying complexities [116,117]. In Fig.…”

Section: B Variation Of Surface Charge Chemical and Zeta Potentialsupporting

confidence: 85%

Self-Consistent Approach to Global Charge Neutrality in Electrokinetics: A Surface Potential Trap Model

Wan

Liao

et al. 2014

Phys. Rev. X

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In this work, we treat the Poisson-Nernst-Planck (PNP) equations as the basis for a consistent framework of the electrokinetic effects. The static limit of the PNP equations is shown to be the charge-conserving Poisson-Boltzmann (CCPB) equation, with guaranteed charge neutrality within the computational domain. We propose a surface potential trap model that attributes an energy cost to the interfacial charge dissociation. In conjunction with the CCPB, the surface potential trap can cause a surface-specific adsorbed charge layer σ. By defining a chemical potential μ that arises from the charge neutrality constraint, a reformulated CCPB can be reduced to the form of the Poisson-Boltzmann equation, whose prediction of the Debye screening layer profile is in excellent agreement with that of the Poisson-Boltzmann equation when the channel width is much larger than the Debye length. However, important differences emerge when the channel width is small, so the Debye screening layers from the opposite sides of the channel overlap with each other. In particular, the theory automatically yields a variation of σ that is generally known as the "charge regulation" behavior, attendant with predictions of force variation as a function of nanoscale separation between two charged surfaces that are in good agreement with the experiments, with no adjustable or additional parameters. We give a generalized definition of the ζ potential that reflects the strength of the electrokinetic effect; its variations with the concentration of surface-specific and surfacenonspecific salt ions are shown to be in good agreement with the experiments. To delineate the behavior of the electro-osmotic (EO) effect, the coupled PNP and Navier-Stokes equations are solved numerically under an applied electric field tangential to the fluid-solid interface. The EO effect is shown to exhibit an intrinsic time dependence that is noninertial in its origin. Under a step-function applied electric field, a pulse of fluid flow is followed by relaxation to a new ion distribution, owing to the diffusive counter current. We have numerically evaluated the Onsager coefficients associated with the EO effect, L 21 , and its reverse streaming potential effect, L 12 , and show that L 12 ¼ L 21 in accordance with the Onsager relation. We conclude by noting some of the challenges ahead.

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Section: B Variation Of Surface Charge Chemical and Zeta Potentialsupporting

confidence: 85%

Self-Consistent Approach to Global Charge Neutrality in Electrokinetics: A Surface Potential Trap Model

Wan

Liao

et al. 2014

Phys. Rev. X

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“…Despite the expected weaker surface charge, the measured ζ potentials are typically of the same order of magnitude as those observed on hydrophilic surfaces [30]. This could in fact arise from small bare surface potentials and slip-induced amplification.…”

Section: Discussionmentioning

confidence: 81%

Liquid friction on charged surfaces: From hydrodynamic slippage to electrokinetics

Joly

Ybert

Trizac

et al. 2006

The Journal of Chemical Physics

209

229

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Hydrodynamic behavior at the vicinity of a confining wall is closely related to the friction properties of the liquid/solid interface. Here we consider, using Molecular Dynamics simulations, the electric contribution to friction for charged surfaces, and the induced modification of the hydrodynamic boundary condition at the confining boundary. The consequences of liquid slippage for electrokinetic phenomena, through the coupling between hydrodynamics and electrostatics within the electric double layer, are explored. Strong amplification of electro-osmotic effects is revealed, and the non-trivial effect of surface charge is discussed. This work allows to reconsider existing experimental data, concerning ζ potentials of hydrophobic surfaces and suggest the possibility to generate "giant" electro-osmotic and electrophoretic effects, with direct applications in microfluidics.

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“…Values for varying from 0.15 to 0.5 have been suggested by various authors (see Hunter 1981;Scales et al 1992;Szymczyk et al 1999). We will assume here a value of 0.3 which is consistent with results of both Sadr et al (2004) and Yao et al (2003).…”

Section: Control Volume Analysismentioning

confidence: 96%

Convective instability of electrokinetic flows in a cross-shaped microchannel

Posner¹,

Santiago²

2006

J. Fluid Mech.

128

132

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We present a parametric experimental study of convective electrokinetic instability (EKI) in an isotropically etched, cross-shaped microchannel using quantitative epifluorescence imaging. The base state is a three-inlet, one-outlet electrokinetic focusing flow configuration where the centre sample stream and sheath flows have mismatched ionic conductivities. Electrokinetic flows with conductivity gradients become unstable when the electroviscous stretching and folding of conductivity interfaces grows faster than the dissipative effect of molecular diffusion. Scalar images, critical applied fields required for instability, and temporal and spatial scalar energy are presented for flows with a wide range of applied d.c. electric field and centre-tosheath conductivity ratios. These parameters impose variations of the electric Rayleigh number across four orders of magnitude. We introduce a scaling for charge density in the bulk fluid as a function of local maximum conductivity gradients in the flow. This scaling shows that the flow becomes unstable at a critical electric Rayleigh number (Ra e, = 205) and applies to a wide range of applied field and centre-tosheath conductivity ratios. This work is relevant to on-chip electrokinetic flows with conductivity gradients such as field amplified sample stacking, flow at the intersections of multi-dimensional assays, electrokinetic control and separation of sample streams with poorly specified chemistry, and low-Reynolds number micromixing.

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Electrokinetics of the silica-solution interface: a flat plate streaming potential study

Cited by 309 publications

References 0 publications

Self-Consistent Approach to Global Charge Neutrality in Electrokinetics: A Surface Potential Trap Model

Self-Consistent Approach to Global Charge Neutrality in Electrokinetics: A Surface Potential Trap Model

Liquid friction on charged surfaces: From hydrodynamic slippage to electrokinetics

Convective instability of electrokinetic flows in a cross-shaped microchannel

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