Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: POSTERS Single Molecules, Biopolymers, Membranes

CPP 9.21: Poster

Monday, February 25, 2008, 16:45–19:00, Poster A

The Effect of electrolytes on interactions in thin aqueous wetting films — •Natascha Schelero, Katarzyna Hänni-Ciunel, and Regine von Klitzing — Stranski-Laboratorium, Institut der Chemie, TU Berlin, Strasse des 17. Juni 124, D-10623 Berlin

The (de)stability and functionality of thin wetting films plays an important role for processes in technical applications. The forces between the opposing interfaces depend on the composition of the film interfaces and of the film fluid. In the present paper the sum of interactions between the film surfaces is determined quantitatively by the disjoining pressure isotherm and it is measured by varying the outer pressure in a thin film pressure balance. Usually, this apparatus is used for disjoining pressure measurements at free-standing foam films (air/liquid/air). In recent studies we showed that it also can be used for the investigation of wetting films (air/liquid/solid) [1]. Water films in presence of 0.1 mM NaCl are stable against negatively charged interfaces like bare Silicon or Silicon coated with negatively charged polyelectrolytes, but unstable against positively charged surfaces. The films become thinner and less stable with increasing ionic strength indicating that the forces within the water film are controlled by electrostatic interactions [2]. The results give a clear evidence for negative charges at the free air/water interface [3]. Further on, the effect of specific ions on the stabilisation by electrostatic interfacial repulsion is investigated. [1] R. v. Klitzing, Adv. Coll. Interf. Sci., 2005,114/115:253 [2] Hänni-Ciunel K. et al., Soft Materials, 2007, 5 (2), 61-73 [3] Ciunel K. et al., Langmuir 2005 21 4790 - 4793