Forschungszentrum Jülich - Research in Jülich 3_2012

Research in Jülich 3|2012 How strongly superglue and magnetic clamps adhere to each other can be determined fairly precisely by mechanical load tests. To date, how strongly a single molecule adheres to a surface could not be directly measured at the microscopic level. Using an atomic force microscope, Jülich physicists have now performed experiments to measure the adhe- sive force of individual molecules on surfaces. Atomic force microscopes usually detect structures by means of a tiny measuring tip. In order to measure the adhesive force, the researchers sharpened the tip to a single atom. With this tip, they lifted a molecule from a surface step by step, until they had completely removed it from the surface, and determined the force required to do so. Combining these experimental data with com- puter simulations allowed the scientists to calculate the strength of the bonds and the contribution of different adhesive forces to these bonds, such as van der Waals forces or a chemical bond. This information could help to verify new theoretical models for interactions be- tween molecules and metals. Force Meter for Molecular Bonds The new HALO research aircraft (High Altitude and Long Range Re- search Aircraft) has gone into opera- tion. Jülich researchers were in- volved in its very first campaign. The TACTS mission (Transport and Com- position in the Upper Troposphere/ Lowermost Stratosphere) is dis- patching six flights from Germany to the Cape Verde Islands. The first of these flights took place at the end of August. During the campaign, re- searchers are measuring the quantity and distribution of important green- house gases such as ozone, carbon dioxide and water vapour in the at- mosphere, especially in the bounda- ry area of the upper troposphere and the overlying lower stratosphere (UTLS). The new findings are expect- ed to help optimize chemistry-cli- mate models. On board the research aircraft are three measuring instru- ments developed by Jülich scientists that detect water vapour and pro- vide information on cloud composi- tion, as well as other data. TACTS is coordinated by scientists from Goethe University Frankfurt. HALO is a joint initiative of Ger- man institutions involved in environ- mental and climate research and the only research platform of its kind in the world. It can fly up to an altitude of 15.5 kilometres and stay in the air for a maximum of ten hours. This al- lows it to reach all regions of the earth’s atmosphere – from the poles to the tropics. The aircraft was offi- cially put into operation by German Federal Research Minister Annette Schavan on 20 August. :: HALO Sets Off into Atmosphere Findings on Leaky Seals Rubber rings and other seals are theo- retically tighter than was previously as- sumed. This is the result of simulations using Jülich supercomputers. Seals can stop liquids leaking as soon as just 42 % of the leak-preventing surfaces are in contact. Previous theories predicted 50 % of the area had to be in contact. In the current simulations, the re- searchers determined the contact area more precisely for the first time by tak- ing into account the elasticity of the sealant material. They found that micro- scopically small peaks of the surface pressed into the soft rubber do not touch all of the seal, but produce addi- tional small gaps. These gaps reduce the contact area, but do not affect the tight- ness of the seal. With their work, the scientists from Forschungszentrum Jülich and Saarland University are contributing to a better understanding of the mechanisms in- volved in leaking seals. Their findings will also allow them to better predict how seals perform as they age. :: The tip of the atomic force microscope, which consists of a single atom, docks onto an oxygen atom (red) of the molecule under investigation from above and lifts it off from a gold surface. Simulation of contact areas in a seal. The gap between the two surfaces allows liquid to escape. 4

Forschungszentrum Jülich - Research in Jülich 3_2012

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