Magnetic-Field-Induced Formation of Superparamagnetic Microwires in Suspension

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.

Formation of magnetically anisotropic composite films at low magnetic fields

“…In fact, in the first fabrication step the dispersed NPs rearrange into the MMA-toluene solution under the effect of the external MF and assemble parallel to its direction. At the same time the occurring MMA polymerization in the vicinity of the assembled NPs links the assembly permanently as also discussed in our previous study [14]. Hence, in the end of the fabrication process, elongated microstructures composed of highly compacted NPs that are permanently linked by the PMMA chains are formed.…”

“…At this temperature, the AIBN decomposes and initiates the MMA thermal polymerization, in the whole volume of the solution. At the same time, the MF causes the assembly of the NPs in the form of MWs which become permanently linked due to the polymerization of MMA also between the assembled NPs, as also described in our previous study [14]. Therefore, the final solution is a highly viscous composite system of PMMA-MWs in toluene.…”

“…So far, different methods have been developed for the fabrication of polymeric composites with magnetic anisotropy. Among them, the magnetophoretic transport and assembly [7,[13][14][15][16][17] is one of the most straightforward methods, where the magnetic nanoparticles (NPs) are directly mixed with polymeric or monomer solutions and upon casting under an external magnetic field (MF) during the solvent evaporation or heat/light-induced polymerization, the particles are assembled in the form of periodic chains oriented parallel to the direction of the applied field.…”

Phosphonated and methacrylated biobased cardanol monomer: Synthesis, characterization and application

“…All of the coatings were characterized by FTIR and water contact angle measurements. As shown in Figure S5 , the typical absorption bands of acrylate monomer at 812 cm -1 (δ C=C ) 37 and at 1643 cm -1 (ν C=C ) 42 are assigned to C=O stretching, C=C vibration and =CH alkene twisting absorptions. After the acrylate formulations were exposed to UV light between 1 and 3 rounds, a significant reduction in the signals of the absorption peaks at 1643 cm -1 and 812 cm -1 was observed, confirming the occurrence of photopolymerization.…”

Imaging Large Iron-Oxide Nanoparticle Clusters by Field-Dependent Magnetic Force Microscopy

“…Various applications in bio-nanomedicine, − bio-separation, , drug delivery, − magnetic hyperthermia, − magnetic resonance, − or magnetic resonance imaging, , rely on the magnetic state of iron-oxide nanoparticles (NPs). − Generally, iron-oxide NPs display small magnetic moments triggering weak magnetic responses in magnetic fields, a drawback for their potential use in applications. , A way to overcome this limitation is to enhance the magnetic moment by increasing the particle size. − One particularly promising solution is the formation of porous or nanoparticulate clusters by self-assembling or self-aggregation. − Hence, inter-nanoparticle interactions within the clusters and the collective behavior can activate higher magnetic moments, − enhancing the magnetic responses while providing larger surface areas for binding functional biomolecules, as needed for instance in drug delivery …”