Acoustic spectroscopy of functionalized carbon nanotubes in magnetic fluid

Abstract Acoustic spectroscopy is used to study the rearrangements of multi-walled carbon nanotubes (MWCNTs) functionalized by Fe3O4 magnetic nanoparticles dissolved in transformer oil under the influence of a magnetic field at various temperatures. Three methods for the application of the magnetic field are used: a jump change, a linear increase or decrease and a constant magnetic field with a change of its orientation to the acoustic wave. The rearrangements of MWCNTs/Fe3O4 to new structures (chains) by the influence of a magnetic field is confirmed by changes in the acoustic attenuation. From the measurement results, the lifetime of the chains after the switch-off of the magnetic field is less than 30 s. Such a rapid change is due to the fact that the nanotube chains are held by magnetic forces, resulting from the same direction of the magnetic moments of bound magnetic nanoparticles. A temperature-dependent hysteresis effect is observed with a linear change of the magnetic field. From our experiments, it follows that the reorientation of MWCNTs by magnetic nanoparticles with the magnetic field was gradual. The effect of the anisotropy of the acoustic attenuation is observed at a magnetic flux density of 200 mT and at various temperatures. Three MWCNT/Fe3O4 concentrations diluted in the transformer oil are used for the measurements and their influences on the structural changes with various developments of the magnetic field are discussed.