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AKB: Biologische Physik

AKB 40: Poster Session II

AKB 40.26: Poster

Mittwoch, 29. März 2006, 16:30–19:30, P3

Counterion profile at a planar charged interface by anomalous x-ray reflectivity — •Klaus Giewekemeyer and Tim Salditt — Institut für Röntgenphysik, Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen

The distribution of counterions in the vicinity of charged surfaces is a theoretically well-studied subject with high relevance for biological problems like protein adsorption to membranes, membrane fusion etc. Although theoretical research on the subject has produced very detailed results that go far beyond the mean field approach (e.g. ion-ion correlation effects, particle volumes), accurate experimental evidence even for the historic Poisson-Boltzmann (PB) mean field result is rare and not completely satisfying. Here an approach to the problem is made by studying the simplest, in the PB theory still analytically solvable case of a planar charged surface at the solid liquid interface. As an experimental realization of this system a DODAB (Di-Octadecyl-Dimethyl-Ammonium-Bromide) monolayer adsorbed to an OTS (Octadeyl-Trichloro-Silane) monolayer bound to a Silicon substrate is chosen. The distribution of the systems Bromide counterions in aequous solution has been probed with resonant small angle x-ray reflectivity. Furthermmore, the variation of the Gouy-Chapman length of the counterion cloud has been studied by changing the charge density of the amphiphilic layer on top of the OTS by mixing the cationic DODAB with zwitterionic DPPC (Di-Palmitoyl-Phosphatidyl-Choline). Selected results and their analysis from an experiment at ESRFs ID 1 beamline are presented.