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Project Ralf Seemann, Barbara Wagner and Dirk Peschka

Structure Formation in Thin Liquid-Liquid Films

The main topic of this tandem proposal is the direct comparison of results from mathematical modeling, analysis and experimental investigations of rupture,dewetting dynamics and equilibrium patterns of a thin liquid-liquid system. The experimental system uses a PS (polystyrene)/ PMMA (polymethylmethacrylate) thin bilayer of a few hundred nanometer, whose liquid properties can be tuned from Newtonian to visoelastic rheological flow behavior by varying the length of the polymer chains. On these small scales, apart from capillary forces and viscous dissipation, intermolecular forces will play an important role in the dynamics and morphology of the interfaces. The mathematical analysis and numerical simulation of adequate thin film models that will be derived from the underlying fluid mechanical equations, will be used through direct comparisons with experiments. Thus, we aim at clarifying also fundamental properties, such as equilibrium contact angles, singularity formation or dewetting rates. This shall form the basis for more complex situations involving evaporation, surfactant monolayers, and slippage, to yield the understanding crucial for many important nanofluidic problems in nature and technology ranging from rupture of the human tear film to the interface dynamics of donor/acceptor polymer solutions used in organic solar cells.

Figure 1: Cross sections through the rims of short chained polystyrene with a molecular weight of 17.4 kg/mol dewetting from polymethylmethacrylate with a molecular weight of 4 kg/mol.
Left images: rim profiles at a dewetted hole radius of 4 µm radius. Right images: later stage of the dewetting process at 10 µm hole radius. top row: experimental results; bottom row: numerical results