Collaborators from the Paul Scherrer Institute PSI and ETH Zurich designed a material that is magnetism-activated in terms of its shape memory. Subjecting the material into a magnetic field retains its shape. This two-component material is comprised of a polymer and droplets of a so-called magnetorheological fluid embedded in it. This new kind of composite material can be applied in the fields of robotics, electronics, aerospace, and medicine. Results of this research are published in the journal Advanced Materials.
Two components comprise the black ribbon. These are a silicone-based polymer and small water droplets and glycerine in which tiny particles of carbonyl iron float. The polymer provides the material's magnetic properties and its shape memory. The shape is retained if the composite material is formed into a specific shape when subjected to a magnetic field. The material returns to its original shape when the magnetic field is removed.
Current composite materials involve polymer and embedded metal particles. The researchers in this study utilized water droplets and glycerine to insert the magnetic particles into the polymer. This arrangement was able to result in a dispersion similar to that in milk.
There is an equal dispersion of the magnetorheological liquid droplets in the new material. "Since the magnetically sensitive phase dispersed in the polymer is a liquid, the forces generated when a magnetic field is applied are much larger than previously reported", explains Laura Heyderman, head of the Mesoscopic Systems Group at PSI and a professor at ETH Zurich. If a magnetic field acts on the composite material, it stiffens. "This new material concept could only come about through teamwork between groups with expertise from two completely different areas - magnetic and soft materials", says Heyderman.
The Swiss Light Source SLS at PSI was utilized to produce X-ray tomographic images. The researchers found out that the length of the droplet in the polymer increase under the influence of a magnetic field and the carbonyl iron particles in the liquid align at least partially along the magnetic field lines. The stiffness of the material is influenced by these two factors.
The fact that the shape memory of the new material is activated by magnetic fields offers further advantages in addition to a higher force. Most shape-memory materials react to changes in temperature. In medical applications, two problems arise as a result. First, excessive heat damages the body's own cells. Second, it is not always possible to guarantee uniform warming of an object that remembers its shape. Both disadvantages can be avoided by switching on the shape memory with a magnetic field.
"With our new composite material, we have taken another important step towards simplifying components in a wide range of applications such as medicine and robotics", says ETH Zurich and PSI materials scientist Paolo Testa, first author of the study. "Our work, therefore, serves as the starting point for a new class of mechanically active materials."
There are different applications for shape-memory materials. An example in the field of medicine is a catheter that is used in minimally invasive operations.
