Flexible and self-assembly anisotropic FeCo nanochain-polymer composite films for highly stretchable magnetic device

Magnetic field induced self-assembly is used to successfully fabricate flexible and anisotropic FeCo nanochain-PDMS composite films. The embedded nanochains are controllable in average length (<200 μm) and width (<2 μm) through optimizing the filler mass fraction and the magnetic field intensity, and an ultra-high aspect ratio of 150 can be achieved. In-situ observations on the growth of a 600 μm long nanochain verify the connection and coarsening mechanism. The composite films are anisotropic along the directions parallel or perpendicular to the alined nanochains or nanobundles. The highest tensile strength in the tension direction perpendicular to the nanochains is 3.20 MPa for the composite film fabricated at 60 mT with 1.0 wt% of filler, which is 85.0% higher than that of the pure PDMS films (1.73 MPa). Different tensile models are proposed to discuss the fracture mechanism, concerning the effectiveness of stress transfer between soft matrix and filler. VSM measurements indicate that the nanochains are easier to be magnetized in parallel geometry due to the larger dipolar coupling. The saturated magnetization (Ms) of nanocomposite films with 1.0 wt% FeCo nanocube filler is 0.45 emu g−1. Such highly flexible, magnetically responsive anisotropic composite films have potential applications especially for highly stretchable devices.