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

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.