The Lamellar Structure In Magnetic Nanocomposite Thin Films

Nanocomposite materials which associate inorganic nanoparticles and polymers with a high degree of organization are highly interesting for their applications in visible light optics (reflectors and guides) and hyper-frequencies (antennae and switches). We focus our study on a complex system combining the self-organization of a symmetrical poly(n-butylmethacrylate)-b– poly(styrene) diblock copolymer (PBMAb- PS) and the orientation properties under magnetic field of inorganic magnetic nanoparticles made of gamma-Fe2O3 iron oxide. To confine those magnetic nanoparticles within the layers of diblock copolymer and thus obtain a lamellar order, it is necessary to coat these nanoparticles with a polymer of the same nature than one bloc of the copolymer. Such a polymeric shell can be grown by initiating polymerization of PS chains at the surface of the nanoparticles ("grafting from") or by adsorbing endfunctionnalized PS chains ("grafting on"). By spin-coating a solution of PBMA-b-PS with or without PS coated nanoparticles in a volatile solvent on a flat silicon wafer and annealing above the glass temperature, we obtain the ordering of the thin film into layers of PBMA alternating with layers of PS doped with nanoparticles. This lamellar order is detected by AFM observation showing characteristic defects such as "islands" and "holes" and by measurements of the lamellar period by Neutron Reflectivity experiments.