“we combined two different classes of materials, namely magnets and polymers, and obtained a composite that retains the properties of both – the ability to manipulate the material with a magnetic field and the elastic properties of the polymer”Laura Heyderman
Scientists have produced a new type of composite material with shape memory that is activated by magnetic fields. While previous shape-memory materials can assume a temporary shape and subsequently recover their original shape on increasing the temperature, this new material consists of a polymer with droplets of embedded magnetorheological fluid, and retains a given shape when positioned in a magnetic field without the need for heat, a functionality that makes it suitable for applications in biomedicine, aerospace, as well as wearable electronics and robotics.
As described in Advanced Materials [Testa et al. Adv. Mater. (2019) DOI: 10.1002/adma.201900561], researchers from the Paul Scherrer Institute PSI and ETH Zurich demonstrated that the two components of the twisted, ribbon-like black material – a silicone-based polymer and containing droplets of a magnetorheological fluid – provide the magnetic magnetomechanical properties of the material as well as its shape memory. The concept is based on a simple emulsion process and is easily extendable to different classes of active fluids and polymer matrices.
When a black band of material is forced into a shape using tweezers and exposed to a magnetic field, the shape is retained even after the tweezers have been removed. Only when the magnetic field is removed does the material return to its original shape. The droplets, containing water and glycerine, are used to introduce magnetic particles into the polymer and ensure that the forces generated when a magnetic field is applied are larger than those previously reported.
Using synchrotron x-ray tomography, it was shown that the length of the droplets in the polymer increases under the influence of a magnetic field, and also that the carbonyl iron particles align at least partially along the magnetic field lines, greatly enhancing the material’s stiffness. One application for this could be altering the stiffness of catheters inserted into blood vessels for minimally invasive operations, so that they only solidify when required and produce fewer side effects when moving through a blood vessel.
As team leader Laura Heyderman told Materials Today, “we combined two different classes of materials, namely magnets and polymers, and obtained a composite that retains the properties of both – the ability to manipulate the material with a magnetic field and the elastic properties of the polymer”.
Encoding a mechanical functionality into a shape-memory material allows actions to be performed without additional components, reducing complexity and improving energy efficiency. This simplification of components serves as the starting point for a new class of mechanically active materials driven by magnetic fields, although the material still needs to be tested in various environments and conditions, and the properties and durability optimized for different applications.
“Magnetic shape-memory material at different length scales: the material is composed of two phases, a polymer and a magnetorheological fluid, which itself is made up of micrometer-size iron particles in an aqueous solvent” (Credit: Paolo Testa)