Percolation-Induced Negative Permittivity in Multi-Walled Carbon Nanotube/Polyimide Metacomposites

Materials with negative permittivity have attracted increasing attention with the development of metamaterials. Here, polyimide/multi-walled carbon nanotube (PI/MWCNT) percolating composites have been fabricated, and, interestingly, the Drude-type negative permittivity behavior is achieved as MWCNT content reached percolation threshold, which is attributed to the plasmonic state of delocalized electrons within the interconnected MWCNTs. In addition, conductivity of composites increases abruptly by almost three orders of magnitudes when MWCNT content reached 1 wt%. Meanwhile, the conduction mechanism changed, suggesting the electrical properties are related to percolation of composites. Moreover, reactance is discussed based on equivalent circuit analysis and the composite with negative permittivity shows inductive character. This work explored the regulation mechanism of negative permittivity in kHz regions and the obtained epsilon-negative metacomposites are promising for applications like electromagnetic shielding and wearable cloaks, etc.