Research report 2005 - Max Planck Institute of Colloids and Interfaces

Ion distribution and foam stability

Motschmann, Hubert

Grenzflächen (Prof. Dr. Helmuth Möhwald)
MPI für Kolloid- und Grenzflächenforschung, Potsdam

Amphiphilic molecules contain a hydrophilic headgroup and a hydrophobic tail. The prevailing molecular asymmetry leads to a spontaneous adsorption of amphiphiles at the air-water or oil-water interface. As a result, the surface tension and the surface rheology are changed. We are using soluble amphiphiles as model systems to study fundamental interactions in colloid and interface science. An example is the distribution of ions at a charged interface. The puzzling ion specific effects are the result of a subtle balance of several competing evenly matched interactions consisting of a complex interplay of electrostatics, dispersion forces, thermal motion, fluctuations, hydration, ion size effects and the impact of interfacial water structure. Furthermore we try to identify correlations between observed macroscopic and the corresponding molecular properties of the adsorbed species. Surfactants enable phenomena such as foaming or emulsions. Foams can only be formed if surface active materials are present. The stability of foams is not yet completely understood and we believe that the surface rheology plays a decisive role. In the last years we developed several novel experiments to study surfactant dynamics and surface rheology.

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