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Keywords:

  • composite materials;
  • magnetic nanoparticles;
  • magneto-sensitivity;
  • polyurethane;
  • poly[ethylene-ran-(vinyl acetate)]

Abstract

The magnetic memory effect (MME) is the ability of magneto-sensitive materials to remember the magnetic field strength (Hdef), at which they were deformed recently. They respond close to Hdef either by recovering their initial shape at a switching magnetic field strength Hsw under stress-free conditions or by building up stress with a peak maximum at Hσ,max under constant strain conditions. This paper explores whether such a MME can be created for polymer-based nanocomposites. The concept is based on temperature-memory polymers (TMP) as matrix, in which silica coated iron(III)oxide nanoparticles (mNP) are dispersed. The MME was explored in a cyclic magneto-mechanical test, in which the nanocomposite sample was elongated to ϵm while being exposed to an alternating magnetic field at Hdef. The magnetic memory was read out by determining Hσ,max or Hsw. A linear correlation between Hσ,max (or Hsw) and Hdef in a range from 15 to 23 kA m−1 at a fixed frequency of f = 258 kHz is observed and demonstrates the excellent magnetic memory properties of the investigated nanocomposites containing either crystallizable or amorphous, vitrifiable domains as controlling units. The deformation ϵm at Hdef can be fixed with an accuracy of more than 72% and the initial shape can be recovered almost completely by more than 86%. The MME allows the design of magnetically programmable devices such as switches or mechanical manipulators.