Magnetic Nanofibers with Core/Sheath Structure

Abstract

MWNTs/Fe3O4 nanocomposites were prepared simply by the coprecipitation method from the solution of ferrous/ferric mixed salt in the presence of MWNTs. The morphology of MWNTs/Fe3O4 nanocomposites was analyzed by HR-TEM, and then the structure and chemical bonding of MWNTs/Fe3O4 nanocomposites were confirmed by XRD and FT-IR analysis. The M-H hysteresis of MWNTs/Fe3O4 nanocomposites shows the superparamagnetic behavior with small remnant magnetization. Magnetorheological fluid was prepared from MWNTs/Fe3O4 nanocomposites dispersed in a mineral oil. The viscosity of MRF increases under magnetic field because the applied field aligns magnetic particles into fibrous structure. Due to the low density of MWNTs, the sedimentation stability of MRF is also improved compared to the MRF based on pure magnetite particles. Field responsive nanofibers with core(MRF)/sheath (polyurethane) structure were fabricated by coaxial electrospinning and the mechanical properties of both with and without magnetic field were measured by tensile tests. Since the load-carrying capacity of MWNTs is outstanding, the tensile stress and the modulus of core/sheath nanowebs are much higher than those of PU nanowebs. When the magnetic fields are applied to core/sheath nanowebs, the mechanical properties improve, but the elongation at break is slightly decreases. Due to the ability to absorb electromagnetic waves, nanowebs containing MWNTs/Fe3O4 nanocomposites can be applied as EMI shielding material. Even in a narrow range of frequencies, core/sheath nanowebs show outstanding EMI shielding properties.