Force-Assembled Fe<sub>3</sub>O<sub>4</sub> Particle Chains in Polyurethane Matrix

Abstract

Despite substantial research efforts, the potential of polymer nanocomposites has still not been fully revealed, mainly due to poor control over the dispersion and alignment of nanoparticles (NPs). Since nanocomposite properties are controlled by the structural variables, it is crucial to achieve control over the NP assembly process.Self-assembly of NPs offers limited control over the NP spatial arrangement. This process results in a poorly controlled variation of simple structures such as agglomerates, clusters and dispersed NPs with the resulting structure strongly dependent a on wide range of thermodynamic parameters.On the other hand, force-assembly exploits interactions between particles induced by external force fields overcoming the thermodynamic ones. Stimulus of external electric, magnetic or electro-magnetic field is applied as the main force controlling the assembly of NPs. Understanding this process gives us the opportunity to create prescribed NP structures with controlled shape, size, and anisotropy by simple change of the force field. Precise control of structure formation on different length scales (from nanoto macro) gives us the opportunity to imitate hierarchical biological structures possessing unique balance of stiffness and toughness.Here, we report on magnetic field force assembly of Fe3O4 nanoparticles in the polyurethane matrix. Resulting NP chain structures were several NP wide and tens of micrometers long aligned along the magnetic force lines. Without the magnetic field, NP agglomerates of random size and shape were formed due to their self-assembly.