The development of materials with magnetically adjustable properties has been presented by a German research team from the Helmholtz-Zentrum Geesthacht (HZG) Centre for Biomaterial Development in Teltow. Triple-shape polymers are able to perform two distinct changes in shape when heated, if the shape changes are programmed beforehand by application of a specific thermomechanical procedure. When heated, the materials change at predefined switching temperatures from the current shape to the first memorized shape and from there to the second memorized shape. By application of magnetic fields with different field strengths the switching temperatures of such composites can be adjusted in a controlled manner.
These novel actively moving “Triple-Shape Nanocomposites” are composed of a polymer matrix consisting of two different crystallisable polymer chain segment types, which are linked by chemical bonds, and embedded iron oxide nanoparticles. Each crystallisable segment type can memorize one specific shape. The magnetic particles get heated by the applied weak, alternating magnetic field and serve thereby as an additional heating source. The higher this energy contribution, the lower the environmental temperature at which the shape changes will occur.
The reported adjustability of the switching temperatures of the nanocomposites is based on the combination of direct heating by increasing the environmental temperature and indirect heating by the exposure of the embedded iron-oxide nanoparticles to an alternating magnetic field. Only this combination of two different heating sources allows a controlled manipulation of the switching temperatures, which are defined as environmental temperatures where the shape changes occur.
The controlled decrease of the switching temperatures by application of weak magnetic fields allows the realization of applications where an initialization of a triple-shape effect solely by environmental heating of the device has not been applicable before.