Novel magnetite-carbon nanofiber hybrids (denoted by “Fe3O4@CNFs”) have been developed by coating
carbon nanofibers (CNFs) with magnetite nanoparticles in order to align CNFs in epoxy using a relatively
weak magnetic field. Experimental results have shown that a weak magnetic field (~50 mT) can align
these newly-developed nanofiber hybrids to form a chain-like structure in the epoxy resin. Upon curing,
the epoxy nanocomposites containing the aligned Fe3O4@CNFs show (i) greatly improved electrical
conductivity in the alignment direction and (ii) significantly higher fracture toughness when the
Fe3O4@CNFs are aligned normal to the crack surface, compared to the nanocomposites containing
randomly-oriented Fe3O4@CNFs. The mechanisms underpinning the significant improvements in the
fracture toughness have been identified, including interfacial debonding, pull-out, crack bridging and
rupture of the Fe3O4@CNFs, and plastic void growth in the polymer matrix.