Blending of soft polymer matrices with nanoparticles has led to nanocomposites with exceptional properties and therefore have a large potential for applications in materials science.1,2 In particular, responsive polymeric nanocomposites that are able to adapt to different surrounding environments are playing an increasingly important role. Due to their unique magnetic properties, superparamagnetic iron oxide nanoparticles are perfectly suitable for the synthesis of magneto responsive nanocomposites.
However, synthesis of homogeneous polymer-NC nanocomposites is still one of the biggest problems, because of the immiscibility of the inorganic nanoparticles with their host matrix in the nanocomposite. Several approaches to overcome this difficulty exist, especially by grafting polymer chains on the particle surface of the same chemical nature as the host matrix.
Nevertheless, an unstable ligand shell often leads to phase separation, resulting in self-assembly of the nanoparticles into a variety of superstructures, thus changing the magnetic properties of the nanocomposite in a hardly reproducible manner. We developed a three-step approach to overcome this problem by introducing a robust ligand shell, which is cross-linked by covalent bonds and, therefore, provides maximum stability. Micellar encapsulation is based on the hydrophobic part of amphiphilic polymers (diblock copolymers) intercalating with the hydrophobic ligand shell of the particle while the hydrophilic part is reaching into the aqueous solution.3 The hydrophilic part often consists of poly(ethylene oxide) (PEO). The stability of the micelles can be further increased by crosslinking the hydrophobic part and this is a crucial parameter for the homogenous distribution of the nanoparticles within the polymer matrix. The crosslinking of the polymer shell by covalent bonds provides maximum stability during mixing step with the host matrix and results in uniform hybrid nanoparticles homogeneously dispersed in a poly(ethylene oxide) matrix. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) investigations demonstrate the presence of mostly single particles and a negligible amount of dyads.
The combination of advanced synthesis and encapsulation techniques using different diblock copolymers and the thiol-ene click reaction for crosslinking the polymeric shell results in homogenous magneto responsive nanocomposites.4
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 E. Pöselt, C. Schmidtke, S. Fischer, K. Peldschus, J. Salamon, H. Kloust, H. Tran, A. Pietsch, M. Heine, G. Adam, et al., ACS Nano 2012, 6, 3346–3355.
 A. Feld, R. Koll, L. S. Fruhner, M. Krutyeva, W. Pyckhout-Hintzen, C. Weiß, H. Heller, A. Weimer, C. Schmidtke, M.-S. Appavou, et al., ACS Nano 2017, 11, 3767–3775.