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CPP: Chemische Physik und Polymerphysik
CPP 19: Poster: New Methods, Thin Polymer Films, Monolayers
CPP 19.20: Poster
Thursday, April 5, 2001, 12:30–15:00, AT1
Reduction of glass transition temperature in thin liquid polymer films and its impact on dewetting dynamics — •Ralf Seemann, Stephan Herminghaus, and Karin Jacobs — University of Ulm, Albert-Einstein Allee 11, D-89069 Ulm
The drastic dependence of the glass transition temperature (TG) of thin polymer films upon their thickness is a puzzle, recently attracting considerable interest. In fact, the dynamics of dewetting of thin liquid polystyrene films is much faster than expected from the bulk, even if the film thickness is much larger than the radius of gyration of the molecules. This is seen from the spinodal break up time as well from the speed of hole growth. We measured TG for our system independently, and introduced a scaling law relating the viscosity to film thickness and temperature. This scaling law is in good agreement with the measured viscosity of the dewetting film, and is also in accordance with the dynamics of the dewetting process as obtained from simulation. The reduction of the TG for thin films can be explained qualitatively from the surface eigenmodes of the viscoelastic polymer melt. The characteristic length scale involved is the ratio of the entropic shear modulus divided by the surface tension, which is in fact typically much larger than the radius of gyration, and is in qualitative agreement with the film thickness at which a noticeable shift of TG sets in.