Abstract: The pair interactions of highly diluted charge-stabilized colloidal suspensions are well explained in terms of Yukawa potentials. The interactions among colloids, however, are mediated by counter ions and are thus inherently many-body in nature. This means that the total interaction of a system of more than two colloids is NOT the sum over all pair wise interaction energies. In order to investigate the deviations from a strict pair wise 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 pair wise 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 of same range as the undisturbed pair-potential. We further explored possible effects many-body interactions can have on macroscopic properties of colloidal suspensions. We show that the solid-liquid phase behavior changes due to the presence of many-body interactions.
Seminarsko predavanje bo v cetrtek, 27. februarja 2003 ob 15:15 uri v seminarski sobi CAMTP na Krekovi 2, pritlicje desno. Vljudno vabljeni vsi zainteresirani, tudi študentje.