We demonstrate the fabrication of polymeric membranes that incorporate a few layers of periodically aligned magnetic microchains formed upon the application of variable magnetic fields. A homogeneous solution containing an elastomeric polymer and a small amount of colloidal magnetic nanoparticles is spin coated on glass slides, thereby forming thin magnetic membranes of ca. 10 μm thickness. Subsequent application of a homogeneous magnetic field results in the orientation of the magnetic clusters and their further motion into the matrix along the field lines forming layers of aligned chains. The study of the kinetics of alignment demonstrates that the chains are formed in the first hour of exposure to the magnetic field. Above all, a detailed microscopy study reveals that the dimensions and the periodicity of the microchains are effectively controlled by the intensity of the magnetic field, in good agreement with the theoretical simulations. This ability to form and manipulate the size and the distribution of chains into the polymeric matrix gives the opportunity to develop multifunctional composite materials ready to be used in various applications such as electromagnetic shielding, or multifunctional magnetic membranes etc.

No abstract

We demonstrate the formation of stable magnetic microwires (MWs) in solution starting from a highly diluted solution of monomer−thermal initiator− superparamagnetic nanoparticles (SMNPs). Under an external magnetic field (MF) the SMNPs get closely packed into wire-like assemblies that become permanently linked due to simultaneous thermal polymerization of the monomer. As the SMNPs assemble in the form of wires under MF, the concentration of the monomer chains adsorbed onto them increases in the near proximity of these assemblies, promoting the polymerization process during heating. This combined process causes the permanent bonding among the SMNPs, forming smooth MWs with metallic character. Detailed microscopic and spectroscopic studies reveal the mechanism of the process and designate the importance of the external MF, the thermal polymerization, and the high dilution factor of the reaction solution for the formation of free-standing uniform wires with controlled size. This method leads to a novel approach to form long magnetic wires with smooth contour and regular shape, which can be used in various fields of applications like in biomedicine, chemistry, fluidics, etc.