Tailoring the recovery force in magnetic shape-memory nanocomposites

Abstract

Composites from magnetic nanoparticles in a shape-memory polymer (SMP) matrix allow a remote actuation of the shape-memory effect by exposure to alternating magnetic fields. At the same time the incorporation of MNP may affect the thermal properties and the structural functions of the SMP. Here, we explored the adjustability of the recovery force as an important structural function in magnetic shape-memory nanocomposites (mSMC) by variation of the programing temperature (Tprog) and nanoparticle weight content. The nanocomposites were prepared by coextrusion of silica coated magnetite nanoparticles (mNP) with an amorphous polyether urethane (PEU) matrix. In tensile tests in whichTprog was varied between 25 and 70 °C and the particle content from 0 to 10 wt% it was found that the Young’s moduli (E) decreased with temperature and particle content. Cyclic, thermomechanical experiments with a recovery module under strain-control conditions were performed to monitor the effect of mNP andTprog on the recovery force of the composites. During the strain-control recovery the maximum stress (σm, r) at a characteristic temperature (Tσ, max) was recorded. By increasing the mNP content from 0 to 10 wt% in composites, σm, r of 1.9 MPa was decreased to 1.25 MPa at aTprog = 25 °C. A similar decrease inσm, r for nanocomposites with different mNP content could be observed whenTprog was increased from 25 °C to 70 °C. It can be concluded that the lower the deformation temperature and the particle content the higher is the recovery force.