Hydrolysis versus ion correlation models in electrokinetic charge inversion: Establishing application ranges

M.L. Jimenez, A.V. Delgado, J. Lyklema

Research output: Contribution to journalArticleAcademicpeer-review

29 Citations (Scopus)

Abstract

In this article, we investigate experimentally a wide range of situations where charge inversion (i.e., overcompensation of the surface charge of a colloidal particle by the countercharge) can occur. To that end, the electrophoretic mobility of sodium montmorillonite, silica, and polystyrene latex as functions of pH and concentration of different salts is presented, and conditions are established where charge inversion occurs. The reason for this study is to provide experimental evidence for distinguishing between two existing models for the explanation of charge inversion. One of these is the specific adsorption of ions located in the Stern layer in combination with a Gouy–Chapman diffuse part of the double layer. The other ion-correlation theories explain the phenomenon in terms of purely physical arguments based on Coulombic pair interactions between ions and surface charges and on excluded volume effects. In distinguishing between these two interpretations, the influence of the pH plays a central role because of its effect on the hydrolysis of multivalent cations. In our experiments, it is found that although 1–2 and 2–2 electrolytes provoke a decrease in the absolute values of the electrophoretic mobilities when their concentration in solution is increased, they never lead to charge inversion, whatever the surface charge or the pH. However, in the case of salts of trivalent cations, electrokinetic charge reversal is often observed above a certain critical electrolyte concentration. In addition, the extent of overcharging increases when the concentration is raised above the critical value. This trend occurs for any system in which the surface charge is pH-independent, as in polystyrene latex and montmorillonite. Most of the results presented here are compatible with the specific adsorption of hydrolyzed metal ions as the main driving force for charge inversion. At low pH, when the hydrolysis of trivalent cations is likely to be absent, overcharging can be attributed to ion correlation effects.
Original languageEnglish
Pages (from-to)6786-6793
JournalLangmuir
Volume28
Issue number17
DOIs
Publication statusPublished - 2012

Fingerprint

electrokinetics
Surface charge
hydrolysis
Hydrolysis
Ions
inversions
Bentonite
Cations
Electrophoretic mobility
Positive ions
Clay minerals
Latexes
Electrolytes
Polystyrenes
montmorillonite
latex
ions
cations
Salts
Correlation theory

Keywords

  • electrical double-layer
  • hydrolyzable cations
  • surface-charge
  • monte-carlo
  • electrolyte
  • montmorillonite
  • silica
  • counterions
  • suspensions
  • equation

Cite this

Jimenez, M.L. ; Delgado, A.V. ; Lyklema, J. / Hydrolysis versus ion correlation models in electrokinetic charge inversion: Establishing application ranges. In: Langmuir. 2012 ; Vol. 28, No. 17. pp. 6786-6793.
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Hydrolysis versus ion correlation models in electrokinetic charge inversion: Establishing application ranges. / Jimenez, M.L.; Delgado, A.V.; Lyklema, J.

In: Langmuir, Vol. 28, No. 17, 2012, p. 6786-6793.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Hydrolysis versus ion correlation models in electrokinetic charge inversion: Establishing application ranges

AU - Jimenez, M.L.

AU - Delgado, A.V.

AU - Lyklema, J.

PY - 2012

Y1 - 2012

N2 - In this article, we investigate experimentally a wide range of situations where charge inversion (i.e., overcompensation of the surface charge of a colloidal particle by the countercharge) can occur. To that end, the electrophoretic mobility of sodium montmorillonite, silica, and polystyrene latex as functions of pH and concentration of different salts is presented, and conditions are established where charge inversion occurs. The reason for this study is to provide experimental evidence for distinguishing between two existing models for the explanation of charge inversion. One of these is the specific adsorption of ions located in the Stern layer in combination with a Gouy–Chapman diffuse part of the double layer. The other ion-correlation theories explain the phenomenon in terms of purely physical arguments based on Coulombic pair interactions between ions and surface charges and on excluded volume effects. In distinguishing between these two interpretations, the influence of the pH plays a central role because of its effect on the hydrolysis of multivalent cations. In our experiments, it is found that although 1–2 and 2–2 electrolytes provoke a decrease in the absolute values of the electrophoretic mobilities when their concentration in solution is increased, they never lead to charge inversion, whatever the surface charge or the pH. However, in the case of salts of trivalent cations, electrokinetic charge reversal is often observed above a certain critical electrolyte concentration. In addition, the extent of overcharging increases when the concentration is raised above the critical value. This trend occurs for any system in which the surface charge is pH-independent, as in polystyrene latex and montmorillonite. Most of the results presented here are compatible with the specific adsorption of hydrolyzed metal ions as the main driving force for charge inversion. At low pH, when the hydrolysis of trivalent cations is likely to be absent, overcharging can be attributed to ion correlation effects.

AB - In this article, we investigate experimentally a wide range of situations where charge inversion (i.e., overcompensation of the surface charge of a colloidal particle by the countercharge) can occur. To that end, the electrophoretic mobility of sodium montmorillonite, silica, and polystyrene latex as functions of pH and concentration of different salts is presented, and conditions are established where charge inversion occurs. The reason for this study is to provide experimental evidence for distinguishing between two existing models for the explanation of charge inversion. One of these is the specific adsorption of ions located in the Stern layer in combination with a Gouy–Chapman diffuse part of the double layer. The other ion-correlation theories explain the phenomenon in terms of purely physical arguments based on Coulombic pair interactions between ions and surface charges and on excluded volume effects. In distinguishing between these two interpretations, the influence of the pH plays a central role because of its effect on the hydrolysis of multivalent cations. In our experiments, it is found that although 1–2 and 2–2 electrolytes provoke a decrease in the absolute values of the electrophoretic mobilities when their concentration in solution is increased, they never lead to charge inversion, whatever the surface charge or the pH. However, in the case of salts of trivalent cations, electrokinetic charge reversal is often observed above a certain critical electrolyte concentration. In addition, the extent of overcharging increases when the concentration is raised above the critical value. This trend occurs for any system in which the surface charge is pH-independent, as in polystyrene latex and montmorillonite. Most of the results presented here are compatible with the specific adsorption of hydrolyzed metal ions as the main driving force for charge inversion. At low pH, when the hydrolysis of trivalent cations is likely to be absent, overcharging can be attributed to ion correlation effects.

KW - electrical double-layer

KW - hydrolyzable cations

KW - surface-charge

KW - monte-carlo

KW - electrolyte

KW - montmorillonite

KW - silica

KW - counterions

KW - suspensions

KW - equation

U2 - 10.1021/la3010773

DO - 10.1021/la3010773

M3 - Article

VL - 28

SP - 6786

EP - 6793

JO - Langmuir

JF - Langmuir

SN - 0743-7463

IS - 17

ER -