Regensburg 2004 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 12: Colloids and Nanoparticles II

CPP 12.5: Talk

Monday, March 8, 2004, 16:45–17:00, H 39

ION DISTRIBUTION AT CHARGED INTERFACES — •Patrick Koelsch and Hubert Motschmann — Max-Planck-Institute of Colloids and Interfaces, Am Muehlenberg, 14476 Potsdam

The distribution of ions close to a charged wall is a classical problem in colloid and interface science. The traditional approach consists in a mean field analysis of the counterion distribution leading to the Poisson-Boltzmann theory. Recently this field has attracted renewed attention with several theoretical papers addressing effects beyond the mean field level such as fluctuations, discreteness of charges or 2D-correlations. These papers reveal certain new features which are not captured in the mean field picture. We already demonstrated, that the combination of nonlinear (suface Second Harmonic Generation SHG) and linear optical technics (Ellipsometry) allows a direct determination of the prevailing ion distribution. A simple analytical expression was derived which can be used to retrieve the number of condensed counterions within the compact or so called Stern-layer. In this contribution we apply this formalism on experimental data gained on aqueous cationic surfactants by varying the counterions in order to quantify specific ion effects at the interface following the Hofmeister series. The derived formalism relates the ellipsometric signal to the surface charge and promises great potential in order to discard or proof recently published theoretical approaches.