Dresden 2003 – wissenschaftliches Programm

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.14: Poster

Donnerstag, 27. März 2003, 15:30–18:00, P1

Direct evidence for three-body interactions in colloidal suspensions — •Matthias Brunner, Jure Dobnikar, Hans Henning von Grünberg, and Clemens Bechinger — Universität Konstanz

The pair interactions of highly diluted charge-stabilized colloidal suspensions are well explained in terms of a Yukawa potential. Because the interactions among colloids are mediated by counterions (and thus being inherently a many-body effect), however, the total interaction of a system of more than two colloids is NOT the sum over all pairwise interaction energies.

In order to investigate these deviations from a strict pairwise additivity, we measured the three-body interaction in a charge-stabilized colloidal suspension. This was achieved by a scanned optical tweezer which provided a one-dimensional trapping potential for two colloidal particles. When a third particle is approached, considerable deviations from a pairwise additive DLVO-description are observed. The deviations can be used to extract the three-body potential as defined by the McMillan Mayer theory. These experimental findings are also compared to Poisson-Boltzmann calculations and show good agreement. The obtained three-body potentials are of similar size and same range as the undisturbed pair-potential and may account for the recently discussed like-charge attraction in charged colloidal suspensions.