Revealing the essential effect mechanism of carbon nanotubes on the thermal conductivity of graphene film

Abstract

The inclusion of carbon nanotubes (CNTs) should increase the thermal conductivity (TC) of graphene films. However, this notion still remains controversial and the effect mechanism of CNTs on the TC of graphene films is uncertain. Here, graphene films with different CNT loadings are fabricated to reveal the effect mechanism of CNTs. After graphitization of the as-obtained films, lattice distortion occurs and the defect density increases from 1.57 × 10¹⁰ cm⁻² to 3.73 × 10¹⁰ cm⁻² due to the addition of CNTs. Moreover, the introduction of CNTs induces the generation of CC bonds between the CNTs and graphene. Molecular dynamic simulation proves that the existence of CC bonds reduces the in-plane thermal conductivity (IP-TC). The measurement results from different equipment further demonstrate the decreasing trend of the IP-TC with the increment of the CNT content. Conversely, the out-of-plane thermal conductivity (OP-TC) increases from 0.5 W (m K)⁻¹ to 3.5 W (m K)⁻¹ and the elastic modulus decreases from 2.86 GPa to 71.69 MPa. Thus, the graphene/CNT hybrid film is more suitable as a thermal interface material at high temperatures (>200 °C), rather than heat spreader materials. The work provides a more in-depth understanding and a new application route for graphene/CNT films.