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SYPF: Struktur und Dynamik in dünnen Polymerfilmen

SYPF 1: Structure and Dynamics in Thin Polymer Films

SYPF 1.10: Hauptvortrag

Donnerstag, 14. März 2002, 15:00–15:30, H37

Controlling Instabilities in Thin Films — •U. Steiner — Department of Polymer Chemistry and Materials Science Center,University of Groningen, Netherlands

The detection of instabilities in thin polymer films allows to measure forces at interfaces that are otherwise difficult to detect. Three examples will be given:

Electrohydrodynamic Instabilities: an electric field perpendicular to a dielectric interface causes the build–up of displacement charges. The increased free energy of this interfacial charge layer causes a exponentially diverging capillary instability. When using a thin film bilayer, this causes the break–up of the films.

Thermomechanical Instabilities: similar to the effect of electric field is a temperature difference applied to a double layer of two materials of different thermal conductivities. In this case, the film instability is caused by the radiation pressure of phonons that are reflected off the interface between the two materials.

Acoustic Casimir Effect: similar to the electromagnetic Casimir effect is the exclusion of a part of the acoustic noise spectrum in a confined geometry. We present a theoretical argument that shows that these acoustic effects are equally important as van der Waals forces in the break –up of thin liquid films.