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Hydrolysis versus ion correlation models in electrokinetic charge inversion: establishing application ranges.
María L Jiménez1, Angel V Delgado, Johannes Lyklema
1Department of Applied Physics, Faculty of Science, University of Granada, 18071 Granada, Spain.
Langmuir : the ACS Journal of Surfaces and Colloids
|April 7, 2012
Summary
Charge inversion in colloidal systems occurs due to specific ion adsorption, particularly with trivalent cations. This study experimentally distinguishes between ion adsorption and ion correlation theories explaining this phenomenon.
Area of Science:
- Colloid and Surface Science
- Electrochemistry
- Physical Chemistry
Background:
- Charge inversion, or overcompensation of surface charge, is a critical phenomenon in colloidal systems.
- Existing theories include specific ion adsorption and ion-correlation effects, requiring experimental validation.
Purpose of the Study:
- To experimentally investigate conditions leading to charge inversion.
- To differentiate between specific ion adsorption and ion-correlation theories for charge inversion.
- To provide evidence for the driving forces behind charge inversion in various colloidal systems.
Main Methods:
- Electrophoretic mobility measurements of sodium montmorillonite, silica, and polystyrene latex.
- Systematic variation of pH and electrolyte concentration (1-2, 2-2, and trivalent cation salts).
- Analysis of how these parameters influence colloidal particle charge and mobility.
Main Results:
- 1-2 and 2-2 electrolytes decreased mobility but did not induce charge inversion.
- Trivalent cation salts induced charge inversion above a critical concentration, with overcharging increasing with concentration.
- pH-independent surface charge systems (latex, montmorillonite) showed similar trends with trivalent cations.
Conclusions:
- Specific adsorption of hydrolyzed metal ions is the primary driver for charge inversion in most tested systems.
- At low pH, ion-correlation effects may contribute to overcharging when cation hydrolysis is minimal.
- Experimental findings support the specific adsorption model for charge inversion, with ion-correlation effects playing a role under specific conditions.
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