CNT@NiO/natural rubber with excellent impedance matching and low interfacial thermal resistance toward flexible and heat-conducting microwave absorption application

The development for functional materials with both excellent electromagnetic wave absorption and high-efficiency thermal conductivity is becoming crucial and urgent due to a great progress in the miniaturization and integration of electronic components. Carbon nanotubes (CNTs) are very promising but still suffer poor microwave absorption and unsatisfactory heat conduction because of their impedance dismatching and interfacial thermal resistance. In this work, a modified atomic layer deposition (ALD) method is developed to fabricate CNT@NiO core shell structures in order to improve electromagnetic impedance matching and decrease interfacial thermal resistance. Uniform NiO coating can be high-efficiency grown onto the surface of CNTs by utilizing O3 and H2O as oxygen source synchronously. The CNT@NiO composites exhibit remarkably improved microwave absorption properties compared to the pristine CNTs. The optimal reflection loss reaches -43.6 dB at 17.5 GHz with a thickness of only 1.3 mm. Moreover, the effective absorption frequency can be regulated by simply adjusting the cycle number of ALD NiO. The remarkable microwave absorption properties may be attributed to the multiple interfacial polarization, good impedance match and multiple reflection and scattering owing to the synergistic effects from well-balanced combination of CNT and NiO. In addition, uniform NiO coating can serve as an intermediate layer between matrix and CNTs to reduce the interface thermal resistance, resulting in the remarkably enhancement of thermal conductivity. With natural rubber (NR) as matrix, CNT@NiO/NR flexible composites can be potential applied in the field of electronic packaging, microwave absorption and thermal management.