Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 73: Solid/liquid interfaces II (focussed session)

O 73.7: Talk

Thursday, March 25, 2010, 17:15–17:30, H33

Electrokinetics and Charge Inversion as studied by Single Colloid Electrophoresis — Ilya Semenov, •Gunther Stober, Periklis Papadopoulos, and Friedrich Kremer — Institute for Experimental Physics I (MOP), University of Leipzig, Linnestrasse 5, 04103 Leipzig, Germany

Single Colloid Electrophoresis (SCE) is employed to measure in a specifically designed microfluidic cell the electrophoretic and electroosmotic mobility for the identical colloid. Charge inversion in dependence on concentration, valency and acidity is observed and is proved to be fully reversible. The results are discussed with in terms of overcharging as caused by ion-ion correlations.

The determination and prediction of the surface charge density of the particle's surface are thus of prime importance. This requires an accurate model for the electric double layer at the solid/liquid interface. The standard electrokinetic model is not accurate in strongly coupled systems. That is, for systems containing multivalent ions, high ionic concentration and/or strong surface charge.

A phenomenon known as charge inversion may be seen in electrokinetic measurements such as electrophoresis in presence of multivalent ions, where the sign of the electrokinetic potential appears to be opposite to the expected one. The interpretation of such a result is still controversial. Often it is explained by specific chemical adsorption of multivalent counter-ions. However, the pure electrostatic interactions, i.e. the ion-ion correlations, can cause overcharging by the strong accumulation of counter-ions in contact with a charged surface.