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- Dissipative structures (2) (entfernen)
When thin layers of polymer solutions dry by solvent evaporation and/or heating from below, the layers can become hydrodynamically instable. As a result various surface structures occur. A great pattern manifold of such structures has been found. By self-organization small surface motions caused by surface tension differences can be amplified, when the ratio of the driving forces to the damping ones characterized by the Marangoni-number exceeds a critical value. Besides greater and hierarchic subdivided cell patterns, periodic line structures with peak-valley-differences of down to 1 nm have been found in the solidified layers. The surface profiles (3D- and line profiles) have been measured by means of a microscope interferometer.
Surface tension-driven Marangoni convection causes the formation of regular surface structures in drying polymer layers. The shape of the surface structures formed during solvent evaporation depends on layer and interfacial dynamic parameters as well as external factors. The influence of a horizontal radial temperature gradient produced by a point heat source below the polymer layer on the diffusion-controlled Marangoni instability has been studied. In the region of the lateral temperature gradient, radial surface flow coupled with the interfacial instability leads to stripe, ladder, chevron and/or labyrinthine surface structures.