Flexible PVDF/carbon materials/Ni composite films maintaining strong electromagnetic wave shielding under cyclic microwave irradiation
In current work, multiwall carbon nanotubes (MWCNTs), graphene nanoplatelets (GnPs) and nickel (Ni chains or flowers) are evenly dispersed in poly(vinylidene fluoride) (PVDF) matrix to fabricate PVDF/MWCNT/GnPs/Ni (chains or flowers) composite flexible films. We then concentrated on the electrical conductivity and electromagnetic interference (EMI) shielding properties of composite films. By elevating Ni (chains or flowers) content, the EMI shielding properties of composite films were improved thanks to an increased electrical conductivity. Furthermore, in the same Ni concentration, the composite film containing Ni chains displayed the inferior electrical conductivity and EMI shielding properties compared with composite film possessing Ni flowers, which resulted from the blocking path of conductive network caused by bigger size of Ni chains. When the composite films are exposed to cyclic microwave irradiation, the electrical conductivity and EMI shielding properties are decreased due to the oxidation of Ni and separation of conductive fillers caused by flowing melting PVDF polymer from heating energy. Moreover, the decrease tendency of composite film containing Ni flowers is quicker than that of composite film with Ni chains. The reason is that smaller size of Ni flowers are easily oxidized and stronger microwave absorption ability. On the other hand, the existence of nickel oxidation on the surface of Ni would prevent further oxidation, which renders the final composite films with stable high EMI shielding properties whether how many times cyclic microwave irradiation performed. It is believed that these PVDF flexible films are proved to be the promising EMI shielding devices with quick heat dissipation used in relatively high temperature under repeatedly harsh microwave irradiation.