Electric Double Layers with Electrolyte Mixtures:  Integral Equations Theories and Simulations

Martín-Molina, Alberto; Quesada‐Pérez, Manuel; Hidalgo‐Álvarez, R.

doi:10.1021/jp053970n

Cited by 37 publications

(31 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4(b)], whereas the measured decreases much slower to a minimum and never reaches b . At high monovalent salt concentrations, competition between monovalent and multivalent ions in the Stern layer [14] and the complexation of a Z ion with one of its counterions, effectively reducing the valence to Z ÿ 1 [15], have been suggested to play roles. At 1 M KCl, monovalent screening in the Stern layer clearly dominates, as is independent of the Z ion concentration there (Fig.…”

Section: Prl 96 224502 (2006) P H Y S I C a L R E V I E W L E T T E mentioning

confidence: 99%

Charge Inversion at High Ionic Strength Studied by Streaming Currents

et al. 2006

View full text Add to dashboard Cite

We report charge inversion, the sign reversal of the effective surface charge in the presence of multivalent counterions, for the biologically relevant regimes of divalent ions and mixtures of monovalent and multivalent ions. Using streaming currents, the pressure-driven transport of countercharges in the diffuse layer, we find that charge inversion occurs in rectangular silica nanochannels at high concentrations of divalent ions. Strong monovalent screening is found to cancel charge inversion, restoring the original surface charge polarity. An analytical model based on ion correlations successfully describes our observations. DOI: 10.1103/PhysRevLett.96.224502 PACS numbers: 47.57.jd, 66.90.+r, 68.08.ÿp Screening by counterions is of fundamental importance in mediating electrostatic interactions in liquids. For multivalent counterions (Z ions, where Z is the ion valency including the sign), a counterintuitive phenomenon is observed: Screening not only reduces the effective surface charge, but it can also actually cause it to flip sign. This socalled charge inversion (CI) has been proposed to be biologically relevant in, e.g., DNA condensation, viral packaging, and drug delivery [1]. CI is not explained by conventional mean-field theories of screening. Recently, an analytical model was proposed that assumes that Z ions form a two-dimensional strongly correlated liquid (SCL) at charged surfaces [2]. This effect is particularly strong for high Z, and was confirmed experimentally for Z 3 and 4 [3]. Experimental evidence has remained inconclusive for the cases Z 2 and mixtures of Z ions with monovalent ions [4], both of which are biologically relevant given that K , Na , and Mg 2 are the most abundant cations in the cell. The main difficulty is that existing experimental probes become unreliable at high concentrations (*10 mM): Electrophoretic mobility measurements suffer from increasingly low signal to noise at higher salt, whereas surface force measurements are complicated by short-range forces.In this Letter, we investigate CI in individual silica nanochannels at high ionic strength by employing streaming currents as a new method. A streaming current is an ionic current that results from the pressure-driven transport of counterions in the diffuse part of the double layer [5], as illustrated in Fig. 1(b). The Stern layer, where the SCL is formed, is generally accepted to be immobile [6]. Consequently, streaming currents provide a direct measurement of the effective surface charge at the diffuse layer boundary. The well-defined rectangular channel geometry allows for straightforward interpretation. Contrary to other methods, streaming currents remain a reliable probe of the surface charge at high salt, up to 1 M in our experiments. We report unambiguous CI by divalent ions at concentrations above 400 mM. Additionally, we resolve the effect of screening by monovalent salt. We find that monovalent ions reduce CI by high-Z ions, and even cancel CI entirely at sufficiently high monovalent ion concentrations. We succ...

show abstract

Section: Prl 96 224502 (2006) P H Y S I C a L R E V I E W L E T T E mentioning

confidence: 99%

Charge Inversion at High Ionic Strength Studied by Streaming Currents

et al. 2006

View full text Add to dashboard Cite

show abstract

“…However, PBT is based on two major assumptions: (i) ionion correlations are neglected (mean field approach) [2][3][4][5][6], and (ii) the charge carriers are assumed to be infinitely small point charges. In this paper we will consider modifications of PBT to account for the second assumption (volume constraints), while-just as in PBT-we will take a mean-field approach, and will not consider correlation effects.…”

Section: Introductionmentioning

confidence: 99%

Counterion volume effects in mixed electrical double layers

Biesheuvel

Soestbergen

2007

Journal of Colloid and Interface Science

175

222

View full text Add to dashboard Cite

“…Double layers play a central role in understanding phenomena arising in a variety of fields such as electrochemistry, solution chemistry, biophysics and colloid science. Increasing theoretical interest is now being paid to electrolyte mixtures rather than single electrolytes [1][2][3][4][5][6][7][8][9][10][11]. The classical approach to treat the electric double layer is via the PoissonBoltzmann (PB) theory which models the ions as point charges moving in a medium of constant permittivity.…”

Section: Introductionmentioning

confidence: 99%