Berlin 2001 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 14: Self Assembled Layered Systems

CPP 14.5: Talk

Thursday, April 5, 2001, 17:05–17:25, 112

Stress relaxation and dewetting in thin liquid viscoelastic films — •Daniel Podzimek, Ralf Seemann, Stephan Herminghaus, and Karin Jacobs — University of Ulm, Albert-Einstein Allee 11, D-89069 Ulm

Nucleation and spinodal dewetting are the main rupture mechanisms for thin liquid films on solid surfaces. In case of nucleation, typical nuclei are e.g. dust particles in the system. Our experimental results show, however, that in a viscoelastic liquid - e.g. a high molecular weight polystyrene film - also stress can induce dewetting. Stress is induced in the polymer due to the preparation process where a polymer solution is drying in the presence of a solid wall. As a result, the polymer chains are quenched into a non-equilibrium conformation. Such a drying process is typical for a thin film preparation, such as spin coating, dip coating, or spraying. We show that the number density of holes can be reduced by a special preparation process, where the melt is given time to equilibrate. The reduction of the number density of holes is observed as function of molecular weight and polystyrene film thickness as well as equilibration time. Moreover, we present a model for the coupling of the free surface waves to the strain field in the film which is able to account qualitatively for the observed film thickness dependence of the hole density, and quantitatively for the width of indentations observed before by other authors.