Dresden 2006 – scientific programme
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DY: Dynamik und Statistische Physik
DY 46: Poster
DY 46.5: Poster
Thursday, March 30, 2006, 16:00–18:00, P1
New Light on Like-Charge Attraction — •Jörg Baumgartl1, Jose-Luis Arauz-Lara2, and Clemens Bechinger1 — 12. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany — 2Instituto de Física, Alvaro Obregón 64, 78000 San Luis Potosí, Mexico
A controversial debate in colloidal science has been launched in 1990 when Kepler and Fraden reported an unusual long-range attractive component in the pair potential of charged colloidal particles. This so-called like-charge attraction (LCA) was only observed in thin sample cells (typical plate separations < 10mm) while the pair-interaction in unconfined suspensions has been experimentally confirmed to be entirely repulsive which is in agreement with Poisson-Boltzmann theory. In the meantime it has been rigorously proven that the observed attraction can not be explained within the framework of mean field theories and several other approaches seem to fail to reproduce the experimental observations. We reinvestigate the pair-potential of charged colloidal particles in confined and unconfined geometries. We demonstrate that optical artifacts caused by the imaging process can lead to minute distortions in the particle distances as obtained by digital video microscopy. Those distortions result in an apparent minimum in U(r) which agrees with respect to its position and depth with the features observed in LCA. After correction of these distortions we obtain - independent of the confinement conditions - entirely repulsive pair interactions which show good agreement with linearized mean field theories. Thus, we can not support attractive components in the pair-interaction of confined colloidal suspensions.