Microwave Absorption in MWNTs-Based Soft Composites Containing Nanocrystalline Particles as Magnetic Core and Intrinsically Conducting Polymer as a Conductive Layer

Microwave absorbers derived using poly(vinylidene fluoride) (PVDF), super paramagnetic nanocrystalline calcium ferrite (CaFe2O4) and multiwall nanotubes (MWNTs) were developed in this study. Effect of in-situ modification of CaFe2O4 and MWNTs with a conducting layer, (polyaniline, PANI) on different properties of the composite has been investigated systematically. Two approaches were investigated here to gain insight into the mechanism of microwave absorption. Firstly, coating PANI onto CaFe2O4 and blending along with MWNTs; secondly, coating PANI onto MWNTs and blending along with CaFe2O4. The electrical and magnetic properties of various composites containing hybrid particles were evaluated. Interestingly, the PVDF composites containing PANI coated CaFe2O4 blended together with MWNTs showed excellent shielding effectiveness (-57 dB at 18 GHz) as compared to the second approach where PANI was coated onto MWNTs and blended along with CaFe2O4. This was discussed here with respect to the relative permittivity and permeability in a wide range of frequency.