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Forschungszentrum Jülich - Annual Report 2011

SharingKnowledge Annual Report 2011 | Forschungszentrum Jülich 63 In Keeping with Nature – Self-Healing Materials Many wounds in plants, animals and hu- mans heal by themselves: a crack in the bark or broken skin repair themselves, even broken bones grow back together again. In the case of steel, concrete and plastics, however, the damage gets worse over time. Machines and build- ings must be maintained on a regular basis and those parts of a machine par- ticularly prone to wear are reinforced from the outset. This costs both materi- al and energy. Scientists at Jülich turn to nature for answers. They aim to create materials that can repair microscopic cracks and other defects by themselves. In develop- ing such self-healing materials, re- searchers from the Jülich Centre for Neutron Science (JCNS) are cooperating with groups of researchers from Germa- ny and the Netherlands in twelve pro- jects within the German Research Foun- dation’s (DFG) priority programme “Design and Generic Principles of Self- Healing Materials”. The programme, which is coordinated by the University of Jena, began in October 2011 and has been granted initial funding of more than € 5 million for three years. Binding together anew The JCNS team – Dr. Ana Bras, Dr. Wim Pyckhout-Hintzen and Dr. Andreas Wischnewski – is working on self-heal- ing polymers, plastics made of long mo- lecular chains. The researchers are de- veloping mechanisms that will allow a material to repair its defects autono- mously on the molecular level. They vary the reactive end groups of mono- mers, in other words the building blocks that make up these chains, and thus in- fluence their binding properties. Neutron scattering is an indispensa- ble method in terms of understanding such self-healing processes on a micro- scopic level. The wavelength and energy of neutrons make them ideal probes for these investigations. Different neutron scattering experiments can be used to analyse the structure and dynamics of hydrogen bonding in polymers. Hydrogen bonds are extremely im- portant for a material’s ability to repair cracks itself. The chain-like molecules are loosely connected to each other via hydrogen bonds. “These bonds can be broken and re-established,” says Ana Bras. “They form a mesh. When it breaks, it can remesh itself again anew.” This is a huge advantage over existing self-healing products, such as bicycle tyres that release a viscous substance when punctured and seal the hole. How- ever, this only works once in a particular spot. The scientists at Jülich, on the oth- er hand, are working on materials that can grow back together time and again. Then one day, we’ll be able to say: A scratch in the paintwork? A crack in the seal? No need to worry – it’ll heal in no time! Model for technology: bark growth seals a wound in a tree trunk.