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Oberflächenreduktion und Entstehung von Wrinkles und Tubuli in Flüssigkristallmembranen
Deutsche Forschungsgemeinschaft (DFG) ;
The dynamics of thin liquid membranes play an important role in many areas of biology or technical applications. Examples include biological cells, soap bubbles and foams, membranes in microfluidic devices or closed liquid crystalline smectic membranes. The latter have the advantage that they are stable over long periods of time, since they do not suffer from evaporation or drainage of the water like soap bubbles. Thus, free-standing smectic films are very well suited as simple model systems of more complex membranes.
They provide access to material properties, such as the coupling of forces and movements in the smectic layer to deformations of this layer, i. e. bulges or folds.
Experimentally, free-floating liquid crystalline films can be produced by the collapse of a catenoid. Initially, the resulting satellite bubble has a hose-like shape, and gradually contracts towards its minimal surface (sphere). The volume of the bubble remains constant, but the surface area is reduced, forcing the material to build new layers.
In addition, a deformation of the smectic film can also be observed in some experiments (wrinkles). It will be investigated how a smectic membrane deforms under lateral forces. In particular, the formation of wrinkles and tubules will be clarified, since their formation cannot be explained by the pure orientation-elastic theory of liquid crystals. It seems obvious that the formation of new layers in smectic liquid crystals under very strong lateral compression of the film must be energetically less effective than the formation of wrinkles. It will also be analyzed how the formation of wrinkles depends on the material parameters of the liquid crystal and its thickness.
It is planned to use more viscous liquid crystals than in previous experiments in order to obtain thicker films up to a few micrometers. These materials will also reduce the relaxation time of the bubble. In this way, the surface reduction and the volume of the bubble are additionally determined in order to continue the work on the development of a model of layer redistributions. A greater variation of the film thickness is very important for checking the predictions of the model for the dynamics of smectic layers. In thicker films, more material from lower layers needs to be restructured and the relaxation time of the bubble should increase.