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![]() by Staff Writers Kiel, Germany (SPX) Sep 03, 2018
Geckos, spiders and beetles have shown us how to do it: thanks to special adhesive elements on their feet, they can easily run along ceilings or walls. The science of bionics tries to imitate and control such biological functions, for technological applications and the creation of artificial materials. A research team from Kiel University (CAU) has now succeeded in boosting the adhesive effect of a silicone material significantly. To do so they combined two methods: First, they structured the surface on the micro scale based on the example of beetle feet, and thereafter treated it with plasma. In addition, they found out that the adhesiveness of the structured material changes drastically, if it is bent to varying degrees. Among other areas of application, their results could be interesting for the development of tiny robots and gripping devices. They have been published in the latest editions of the scientific journals Advanced Materials and ACS Applied Materials and Interfaces. Elastic synthetic materials such as silicone elastomers are very popular in industry. They are flexible, re-usable, cheap and easy to produce. They are therefore used for example as seals, for insulation or as corrosion protection. However, due to their low surface energy, they are hardly adhesive at all. This makes it difficult, for example, to paint silicone surfaces.
Surfaces with a mushroom-like microstructure adhere much better Their example to mimic is the surface structure of certain male leaf beetles (Chrysomelidae), looking like mushrooms. In two recent studies, they discovered that silicone elastomers adhere best if their surface is modified into mushroom-like structures and thereafter specifically treated with plasma. The electrically-charged gas which is the fourth state of matter, alongside solids, liquids and gases. Thus, the researchers combined a geometrical and a chemical method, to imitate biology. In addition, they showed that the degree of curvature of the materials affects their adhesion. "Animals and plants provide us with a wealth of experience about some incredible features. We want to transfer the mechanisms behind them to artificial materials, to be able to control their behaviour in a targeted manner," said the zoologist Gorb. Their goal of a reversible adhesion in the micro range without traditional glue could make completely new application possibilities conceivable - for example in micro-electronics.
During experimental tests silicones are curved "In this way, we were able to demonstrate that silicone materials with a mushroom-like structure and curved concave have the double range of adhesive strength," said doctoral researcher Emre Kizilkan, first author of the study. "With this surface structure, we can vary and control the adhesion of materials the most."
Exact parameters for material-friendly plasma treatment To find out how plasma treatments can significantly improve the adhesion of a material without damaging it, the scientists varied different parameters, such as the duration or the pressure. They found that the adhesion of unstructured surfaces on a glass substrate increased by approximately 30% after plasma treatment. On the mushroom-like structured surface the adhesion even increased by up to 91%. "These findings particularly surprised us, because the structured surface is only half as large as the unstructured, but adhesion enhancement was even three times better after the plasma treatment," explained Kizilkan. What happens when the treated and non-treated structured surfaces are removed from the glass substrate show the recordings with a high-speed camera: Because of its higher surface energy the plasma-treated microstructure remains fully in contact with the surface of the glass for 50,6 seconds. However, the contact area of the untreated microstructure is reduced quickly by around one third during the removal process, which is why the microstructure completely detaches from the glass substrate after 33 seconds already (Figure 3).
Especially suitable for applications in microelectronics The findings of the Kiel working group have already resulted in the development of an extremely strong adhesive tape, which functions according to the "gecko principle", and can be removed without leaving any residue.
![]() ![]() Chemists make breakthrough on road to creating a rechargeable lithium-oxygen battery Waterloo, Canada (SPX) Aug 30, 2018 Chemists from the University of Waterloo have successfully resolved two of the most challenging issues surrounding lithium-oxygen batteries, and in the process created a working battery with near 100 per cent coulombic efficiency. The new work, which appears this week in Science, proves that four-electron conversion for lithium-oxygen electrochemistry is highly reversible. The team is the first to achieve four-electron conversion, which doubles the electron storage of lithium-oxygen, also known as ... read more
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