Achieving wideband microwave absorption properties in PVDF nanocomposite foams with an ultra-low MWCNT content by introducing a microcellular structure

In this study, novel poly(vinylidene fluoride) (PVDF)/multiwalled carbon nanotube (MWCNT) nanocomposite foams with various foaming degrees (void fractions) were prepared using a home-made batch foaming process. The effects of the foaming degree in the range of 45.7% to 84.3% on the electrical conductivity, the dielectric permittivity, and the microwave absorption (MA) properties of the nanocomposite foams were investigated in great detail. The electrical conductivity declined linearly with an elevated void fraction, and the PVDF/MWCNT foams with a void fraction below 50% showed a higher electrical conductivity than the unfoamed PVDF/MWCNT nanocomposite counterpart. The dielectric permittivity was also effectively tuned by the foaming degree. Consequently, it could adjust the impedance match to promote MA. The PVDF/MWCNT foam with a void fraction of 69.5% (FC3) exhibited outstanding MA properties. An effective bandwidth (reflection loss below -10 dB, and 90% microwave attenuation) of 8.5 GHz in the measured frequency of 18-26.5 GHz was obtained. A minimal reflection loss (RL) of -34.1 dB could be seen with a thickness of 1.7 mm. The excellent MA properties of these lightweight foam absorbers with ultra-low MWCNTs in the PVDF polymer were attributed to the good impedance match, the greater interfacial polarization, the high conduction loss, and the multiple reflection and scattering mechanisms.