Improved thermal conductivities of vertically aligned carbon nanotube arrays using three-dimensional carbon nanotube networks

Vertically aligned carbon nanotube (VACNT) arrays are considered promising thermal interface materials (TIM) due to their superior vertical thermal conductivity. However, the weak interaction between adjacent carbon nanotubes (CNT) leads to the change in orientation of the CNT during polymer infiltration. Therefore, the thermal conductivity of a CNT array/polymer composite does not reach the expected value. Simultaneously, the air gap between adjacent CNT hinders the in-plane heat transfer, and both of the above aspects significantly reduce the thermal conductivities of VACNT-based TIM. In this study, we proposed a novel three-dimensional CNT (3DCNT) network structure comprising VACNT crosslinked by randomly-oriented secondary CNT to provide several in-plane phonon paths and maintain the structural stability of the CNT arrays during polymer infiltration. The network structures formed by the secondary CNT were compared for two different growth times: 10 and 20 min. The 3DCNT network that grew for 20 min exhibited a denser network structure compared to the network that grew for 10 min. The vertical thermal conductivity and horizontal thermal conductivity of the 3DCNT20/Polydimethylsiloxane (3DCNT20/P) composite was 544.77% and 56.06% higher than those of the IVACNT/P composites, respectively.