Researchers at the Paul Scherrer Institute PSI and ETH Zurich have developed a new material that retains a certain shape when placed in a magnetic field. It is a composite material consisting of two components. Unlike previous materials with memory of the shape, it consists of a polymer and embedded drops of the so-called magnetoreological fluid. Fields of use for this new series of composite materials include medicine, aerospace, electronics and robotics. Researchers now publish their results in a scientific journal Advanced materials.
It looks like a magic trick: the magnet moves away from the black, twisted band, and the band releases without any effect (see video). What magic looks like can be explained by magnetism. The black ribbon consists of two components: a silicone-based polymer and a small drop of water and glycerin in which fine particles of carbonyl float. The latter provide the magnetic properties of the material and its memory of the shape. If the composite material is forced into a certain shape with a tweezer and then exposed to the magnetic field, it maintains its shape even when the tweezers are removed. Only when the magnetic field is removed the material returns to the original shape.
So far, comparable materials have been composed of polymer and embedded metal particles. Instead, researchers at the PSI and ETH Zurich used water droplets and glycerin to insert magnetic particles into the polymer. Thus, they created a dispersion similar to that in milk. In the milk, fine fat droplets are finely dispersed in aqueous solution. They are essentially responsible for white.
Similarly, the drops of the magnetoreological fluid are finely distributed in the new material. "Since the magnetically sensitive phase is scattered in the polymer, the liquid, the forces generated by using the magnetic field are much larger than previously reported," explains Laura Heyderman, head of the Mesoscopic Systems group at the PSI and professor at ETH Zurich. If the magnetic field acts on a composite material, it solidifies. "This new material concept can only be achieved by teamwork between teams with expertise in two totally different areas – magnetic and soft materials," says Heyderman.
Design a memory with alignment with a magnetic field
Researchers studied new material with the help of the Swiss SLS on a light source. X-ray tomographic images produced by this light source have found that the length of the droplets in the polymer is increased under the influence of the magnetic field and that the particles of carbonyl in the liquid at least partially align along the lines of the magnetic field. . These two factors increase the stiffness of the material we are testing up to 30 times.
The fact that the memory of the shape of the new material is activated by magnetic fields has additional advantages in addition to the force majeure. Most of the memory-shaped materials react to temperature changes. There are two problems in medical applications. First, excessive heat damages one's own body cells. Secondly, it is not always possible to ensure a uniform heating of an object that remembers its shape. Both defects can be avoided by incorporating shape memory with a magnetic field.
Mechanically active materials for medicine and robotics
"With the new composite material, we have made another important step towards simplifying components in many applications, such as medicine and robotics," says ETH Zurich and PSI material scientist Paolo Testa, the first author of this study. "Our work is therefore the starting point for a new class of mechanically active materials."
Numerous applications in medicine, space flights, electronics, and robotics are possible for materials with memory shape. For example, catheters that change stiffness when pushed through the blood vessels to a surgical site during minimal invasive surgery. In space exploration, materials with memory are shaped in demand for tires for rover vehicles that inflate or fold themselves. In electronics, soft functional materials can be used in flexible electrical or data cables in load-bearing and robotic devices that can perform mechanical movements without the engine.
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Paolo Testa et al., The magnetically-addressable memory form and curing in a composite elastomer, Advanced materials (2019). DOI: 10.1002 / adma.201900561
New material with magnetic memory of shape (2019, June 5)
June 5, 2019
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