Polyvinyl alcohol/carbon fibers composites with tunable negative permittivity behavior

Random composites with negative permittivity behavior have drawn increasing attention due to their great unique properties. However, there is an urgent requirement in modulating negative permittivity for practical applications. In this study, a novel design approach to tunable negative permittivity according to the regulation of insulating component was proposed. Polyvinyl alcohol (PVA) was introduced into the graphitizing carbon fibers (CFs) skeleton by an impregnation process to prepare CFs/PVA composites. When the content of PVA reached 35.4 wt%, the CFs skeleton was thoroughly covered with insulating PVA film. Along with the great change of microstructure, the Drude-like negative permittivity of the resulting composites decreased by several orders of magnitude and showed a low plasma frequency, which was attributed to the dilution of electron density. Further investigation revealed that the negative permittivity was in association with the inductive character, resulting from the conductive closed paths among the CFs/PVA composites. The tunable negative permittivity in CFs/PVA composites has great potential applications in electromagnetic shielding.