Multi-strategy modulation towards negative dielectric properties in Ag nanoparticle-immobilized carbon fiber felt metacomposites

In this work, Ag nanoparticle-immobilized carbon fiber felt metacomposites (CFF@PDA-Ag) were first fabricated by a chemical-plating method to achieve multi-strategy modulation of their negative dielectric properties. Three routes including Ag nanoparticle content regulation, heat treatment and compression were developed, and their effects on the negative dielectric performance were investigated. It was found that with the increase of deposited Ag nanoparticles, negative permittivity was achieved for the metacomposite with 15 wt% Ag nanoparticles (CFF@PDA-Ag15), resulting from the formation of three-dimensional conductive networks. After heating at 500 °C, the permittivity of CFF@PDA-Ag11 changed from a positive to negative value, which was attributed to its enhanced ac conductivity owing to the grain activation and interparticle bonding of melted Ag nanoparticles. In addition, the results indicated that the dynamic process also adjusted its dielectric properties. After compression, negative permittivity of CFF@PDA-Ag11 was observed and the corresponding absolute value increased with further compression. In addition, the Drude and parallel models composed of conductive carbon fibers and an air phase were used to explain the regulation mechanism of negative permittivity. This work developed a multi-strategy method for achieving adjustable negative permittivity based on Ag nanoparticles, and demonstrated its importance and significance for the development of novel metacomposites.