Abstract: For the advancement of miniaturized and highly integrated electronics, it is essential to develop materials with excellent electrical insulation, electromagnetic protection, and heat dissipation. However, the development of such materials faces critical challenges due to the incompatibility of multiple functions. Herein, we pioneered the design of semiconductor α-MnO₂/semi-metal β-MnO₂ nanofibers (NFs) as a multifunctional filler with a synergistic enhancement in electrical insulation, electromagnetic protection, and heat dissipation. The NFs are obtained from a facile one-step hydrothermal route, and their phase interfaces, length/diameter ratios, and defects are precisely modulated by hydrothermal temperature and MnSO₄ concentration. Results show that the α-MnO₂/β-MnO₂ NF-based thermoplastic polyurethane (TPU) films, benefiting from excellent acoustic matching and effective thermal transfer paths, have a high heat conductivity of 8.05 W/(m K) at a low load of 10 wt%, which is 1.25-175 times as high as those of other previously reported fillers. Moreover, they demonstrate excellent flexibility and electrical insulation properties. Besides, the NFs exhibit a wide-band microwave absorption (3.68 GHz/mm) and radar cross-section (RCS) reduction value of up to 40.70 dB m² under a low load of 30 wt% and a small thickness of 1.5 mm, exceeding most other absorbers. The boosted microwave absorption could be credited to the cooperative effect of their excellent matching, strong attenuation, diverse polarizations, multiple microwave scattering resulting from the abundant defects, and tunable phase interfaces and draw ratios. Further theoretical analyses of their phonon density of states, density of states, and electric field distribution confirm their thermal transfer and polarization mechanisms. These findings provide a new idea for designing and preparing semiconductor/semi-metal multifunctional materials for application in the electronics industry.

Key words: α-MnO2/β-MnO₂ nanofibers, Microwave absorption, Radar stealth, Heat dissipation, Collaborative enhancement mechanism, Calculations of the DOS and PDOS