14 Externe wissenschaftliche Einrichtungen
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/15
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Item Open Access Nanoscale adhesion of individual gecko spatulae explored by atomic force microscopy(2006) Huber, Gerrit; Arzt, Eduard (Prof. Dr. phil.)Attachment mechanisms of animals that can cling to walls and even walk on ceilings have drawn a significant amount of scientific and public attention. The gecko is one of the heaviest and best clinging animals and it has developed intricate hierarchical structures consisting of toes (millimeter dimensions), lamellae (400-600 µm size), setae (micron dimensions) and spatulae (~ 200 nm size). At first this work gives the reader a theoretical background of the techniques used and the underlying physical principles. By means of these techniques the adhesion force for individual spatulae on glass at ambient conditions could be measured and was found to be about 10 nN. This became only possible using the milling facility of a focused ion beam microscope for specimen preparation. The pull-off force was additionally measured as a function of various parameters (air humidity, surface chemistry and surface roughness) and it turned out that the gecko adhesion was remarkably influenced by the presence of water. The pull-off forces were proportional to the relative humidity varied inside an air tight container and increased with decreasing water droplet contact angle of the wafer used. The data obtained were modeled theoretically to explain the observed adhesion phenomena. Two physical theories were presented which are based on concepts of macrocapillarity and the effect of water monolayers on the van der Waals interaction. Both theories showed good agreement with the experimental data. The pull-off forces were also sensitive to the substrate topography. In cases where the surface roughness was in the critical range of the spatula size, presumably imprecise contact formation led to a distinct minimum of the measured adhesion values compared to smoother or rougher surfaces. Furthermore the mechanical properties of single setae could be determined for the first time. The hairs were mechanically tested by three methods: (a) in situ tensile tests using a focused ion beam microscope, (b) three-point bending tests using atomic force microscopy (AFM) and (c) nanoindentation. The results presented in this work shed new light on the nanomechanisms of gecko’s attachment and will help in the rational design of artificial bio inspired attachment systems.