Flexible PVDF/carbon materials/Ni composite films maintaining strong electromagnetic wave shielding under cyclic microwave irradiation

In the current work, multiwalled carbon nanotubes (MWCNTs), graphene nanoplatelets (GnPs) and nickel (Ni chains or flowers) were evenly dispersed in poly(vinylidene fluoride) (PVDF) matrices to fabricate PVDF/MWCNT/GnPs/Ni (chain or flower) composite flexible films. We then concentrated on the electrical conductivity and electromagnetic interference (EMI) shielding properties of the composite films. By increasing the Ni (chain or flower) content, the EMI shielding properties of the composite films were improved due to increased electrical conductivity. Furthermore, at the same Ni concentration, the composite film containing Ni chains displayed inferior electrical conductivity and EMI shielding properties compared with the composite film possessing Ni flowers, which resulted from the blocking path of the conductive network caused by the bigger size of Ni chains. When the composite films were exposed to cyclic microwave irradiation, the electrical conductivity and EMI shielding properties decreased due to the oxidation of Ni and separation of conductive fillers caused by flowing melting PVDF polymers from heating energy. Moreover, the decreasing tendency of the composite film containing Ni flowers was quicker than that of the composite film with Ni chains. The reason was that Ni flowers of smaller size were easily oxidized and possessed stronger microwave absorption ability. The occurrence of nickel oxidation on the surface of Ni could prevent further oxidation, which rendered the final composite films with stable high EMI shielding properties irrespective of how many times cyclic microwave irradiation was performed. These PVDF flexible films have been proven to be promising EMI shielding devices with quick heat dissipation used at a relatively high temperature under repeated harsh microwave irradiation.