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Like Charge Attraction

A controversial debate in colloidal science has been launched about ten years ago when several groups reported an unusual long-range attractive component in the pair potential of charge stabilized colloidal particles. This so-called like-charge attraction (LCA) was only observed in thin sample cells while the pair-interaction in unconfined suspensions has been experimentally confirmed to be entirely repulsive. Despite additional theoretical attempts to understand this phenomenon, however, LCA remains a persistent mystery. 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 find – independent of the confinement conditions – entirely repulsive pair interactions which show good agreement with linearized mean field theories.

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