Berlin 2005 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 13: Selforganized and supramolecular assemblies II

CPP 13.2: Vortrag

Montag, 7. März 2005, 11:30–11:45, TU C243

An experimental route to Hofmeister. — •Patrick Koelsch and Hubert Motschmann — Max-Planck-Institute of Colloids and Interfaces, Am Muehlenberg, 14476 Potsdam, Germany

The distribution of ions close to a charged wall is a classical problem in colloid and interface science. The complex interplay of electrostatics, dispersion forces, thermal motion, fluctuations, hydration, ion size effects and the impact of interfacial water structure makes it hard or even impossible to identify an universal law. The diversity of specific ion effects as manifested by the Hofmeister series of ions is a direct consequence of the subtle interplay of forces. Recently this field has attracted renewed attention as reflected by a special edition in Current Opinion of Colloid and Interface Science.

We already demonstrated, that the combination of nonlinear (surface Second Harmonic Generation SHG) and linear optical techniques (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. We applied 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. In this contribution we will compare our experimental data with recently done simulations which take into account the polarizability or in other words the structure of water at interfaces.