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PV: Plenarvorträge

PV VIII

PV VIII: Plenarvortrag

Mittwoch, 24. März 2004, 14:30–15:00, Aula

Dynamic properties of liquid films — •Dominique Langevin — Laboratoire de Physique des Solides, UMR 8502 - Université Paris-Sud, Bât. 510 - 91405 Orsay cedex — Trägerin des Prix Gentner-Kastler

Surfactant molecules adsorb at liquid interfaces forming monomolecular layers that give remarkable properties to these surfaces. They allow in particular to stabilize freely suspended liquid films, the so called “soap films”, similar to those that cover the bubbles surface in foams. When the liquid possesses a microstructure, and when the film surfaces are close enough (less than 100nm), a film stratification (ordering) is observed. We have used aqueous solutions of ionic polymers (polyelectrolytes) that form networks in bulk when the polymer concentration is high enough. Such liquids also order when confined, at the difference of neutral polymers, where no long range electrostatic interactions are present. We have measured both the forces between surfaces, that are oscillatory, and the stratification kinetics. When the polymer is co-adsorbed with the surfactant at the surface, the local viscosity is higher than the bulk solution viscosity, and when the polymer is not adsorbed, the viscosity is smaller. This is in agreement with other types of measurements of the viscosity of confined fluids with different boundary conditions at the surfaces (slip or no-slip). The film rupture will also be discussed.

References

D. Langevin, “Stratification of foam films made from polyelectrolyte solutions”, Eur. Phys. J. E 5, 2001, 81.

C. Marquez, S. Guillot, D. Langevin, “Stratification Phenomena in Thin Liquid Films Containing Polyelectrolytes and Stabilized by Ionic Surfactants”, Macromolecules 36, 2003, 8506.