The effect of polyethylenimine on the microwave absorbing properties of a hybrid microwave absorber of [Fe.sub.3][O.sub.4]/MWNTs

The hybrid microwave absorber of [Fe.sub.3][O.sub.4]/ multi-walled carbon nanotubes (MWNTs)modified with polyethylenimine (PEI) polymers was fabricated by chemical co-precipitation. The structure and morphology of hybrids are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electronmicroscopy (TEM). The effect of PEI on the distribution of [Fe.sub.3][O.sub.4] nanoparticles and the microwave absorbing properties of hybrid microwave absorber of [Fe.sub.3][O.sub.4]/MWNTs were investigated. The TEM results show that [Fe.sub.3][O.sub.4] nanoparticles are attached homogeneously on MWNTs, which indicates that the adding of PEI is effective to control the distribution of [Fe.sub.3][O.sub.4] nanoparticles on the surface of MWNTs. The microwave absorbing properties results show that the maximum reflection loss (RL) of PEI modified [Fe.sub.3][O.sub.4]/MWNTs hybrids is improved significantly, which is -30.69 dB at 7.24 GHz and -10 dB bandwidth is 1.84 GHz. However, the RL of the [Fe.sub.3][O.sub.4]/MWNTs without PEI is -21.96 dB at 7.02 GHz and -10 dB bandwidth is 1.2 GHz.