Directed assembly of magnetic nanoparticles in polymers: The formation of anisotropic plastic films containing aligned nanowires

We present a facile technique for the preparation of plastic films containing aligned magnetic nanowires with anisotropic behavior. Solutions of magnetic nanoparticles mixed with polymers are drop casted on a substrate under the application of a weak magnetic field, and upon solvent evaporation the nanoparticles are assembled following the field's direction forming thus aligned nanowires into the polymer. The application of the magnetic field in different time intervals reveals the kinetics of the nanowires formation in the film, while microscopy techniques reveal their morphology and their positioning in the film. The resulting nanocomposites exhibit magnetic and mechanical anisotropy. The efficiency and universality of the method is proved by the assembly of the magnetic nanoparticles with diverse polymers, heterostructures and organic molecules resulting in composite materials for a wide range of applications. Finally, the method is successfully applied during the photopolymerization process, allowing the formation of patterns with aligned nanowires.