Radio frequency epsilon-near-zero properties interpretation via CNT/PVDF composites

Realization and interpretation of epsilon-near-zero (ENZ) materials in the radio frequency region have been a research hotspot in recent years. Further understanding the mechanism that how the permittivity transfers from positive or negative to zero will strengthen the basis for preparing materials with ENZ properties. In this study, polyvinylidene fluoride (PVDF) was hot pressed together with multi-walled carbon nanotubes (MWCNTs) at varying contents after milling to realize ENZ properties. Phase composition, microstructure, and electrical properties were analyzed to reveal the transition mechanism of ENZ properties. With the increase in MWCNT concentration, a three-dimensional conductive network consisting of MWCNTs gradually forms within the PVDF matrix. Thus, the primary electron motion mode transitions from electric resonance and polarization before the construction of the conductive network to unrestricted movement afterward, therefore leading to a dramatic increase in electric conductivity in the way of percolation. Furthermore, the permittivity exhibited various types of dispersion behavior with different MWCNT concentrations, which can be described by the Drude–Lorentz or Debye–Drude hybrid model. This work provides further insight into the mechanism of ENZ properties and inspires perspectives for material design.