Shape Anisotropic Chain‐Like CoNi/Polydimethylsiloxane Composite Films with Excellent Low‐Frequency Microwave Absorption and High Thermal Conductivity

Abstract The demand for low‐frequency microwave absorption materials is becoming more and more urgent. Novel shape anisotropy chain‐like CoNi is fabricated using polyvinylpyrrolidone as a shape‐directing agent via solvothermal method, which is then mixed with polydimethylsiloxane (PDMS) to prepare corresponding multifunctional chain‐like CoNi/PDMS composite films. Shape anisotropy and strong magnetic coupling effect of chain‐like CoNi enhance natural resonance and magnetic loss capability. The minimum reflection loss (RL min ) is −50.5 dB and low‐frequency effective absorption bandwidth (EAB) is 1.04 GHz (2.64–3.68 GHz) at 3.9 mm for chain‐like CoNi. The corresponding 18 vol% chain‐like CoNi/PDMS composite films present optimal low‐frequency microwave absorption performance with RL min of −56.7 dB and low‐frequency EAB of 1.04 GHz (2.96–4.00 GHz) at 4.1 mm, which is far superior to 18 vol% spherical CoNi/PDMS composite films with RL min of −9.5 dB. Meantime, the in‐plane and inter‐plane thermal conductivity coefficients of 18 vol% chain‐like CoNi/PDMS composite films are 2.05 and 0.61 W m −1 K −1 , about 1.5 times higher than 18 vol% spherical CoNi/PDMS composite films (1.36 and 0.42 W m −1 K −1 ), also 220% and 190% higher than pure PDMS (0.64 and 0.21 W m −1 K −1 ). This composite films with low‐frequency microwave absorption and thermal conductivity can broaden applications in 5G communications and flexible electronics.