Evolution of fractal-like surface structures in layers of polyacrylonitrile solutions by interfacial dynamic processes |
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Authors: | Weh Lothar Venthur Astrid |
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Institution: | Federal Institute for Materials Research and Testing, Laboratory V 4.2, Unter den Eichen 44-46, 12200 Berlin, Germany. lothar.weh@bam.de |
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Abstract: | Solvent evaporation causes concentration and temperature gradients at the free surface of a coating polymer solution. Thereby surface-tension-driven flows can result in a surface instability with regular structures within the layer. Different types of surface structures can occur at spots with thickness differences. One can find fractal-like structures especially in the edge zone of a layer. The evolution of such fractal-like structures at the surfaces of coating solutions of polyacrylonitrile (PAN) in dimethylformamide (DMF) during layer hardening is examined. Condensation of water on the surface of the fluid layer exerts a strong influence on the formation of these structures. Solutions of PAN in DMF are important for the production of ultrafiltration membranes. Such membranes are produced by precipitation in a water bath after a short open time. |
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