Theoretically designed epsilon-negative materials: Ni nanoparticles encapsulated CNTs and their magnetic driven properties

Epsilon-negative materials (ENMs), especially the materials with a weakly negative permittivity, hold significant value in various applications including electromagnetic absorption, solar energy harvesting, and sensing technologies. In this study, nickel (Ni) nanoparticles were synthesized and encapsulated within carbon nanotubes (Ni@CNTs). Subsequently, films composed of polyvinyl alcohol (PVA) and Ni@CNTs were fabricated (PVA/ Ni@CNTs), demonstrating favorable magnetic driven performance and a broadband weakly negative permittivity. The negative permittivity was about -1500 from 10 kHz to 1 MHz. The presence of pi electrons in carbon materials enhanced carrier mobility, providing the obtained negative permittivity with the advantage of low dispersion. Additionally, a noticeable polarization phenomenon took place at the interface of the two phases (PVA and Ni@CNTs), significantly increasing the positive permittivity to neutralize the negative permittivity. Moreover, this work firstly introduces magnetic-driven soft ENMs, broadening practical applications of such materials to magnetic-driven soft actuators and robotics. Theoretical calculations offer explanations of the mechanism, providing a foundation for designing the next generation of ENMs.