Highly deformable thermal interface materials enabled by covalently-bonded carbon nanotubes

The exceptional thermal conductivity of individual carbon nanotubes have rarely materialized in bulk materials mainly due to the large thermal contact resistance between carbon nanotubes (CNTs). This can be attributed to weak van der Waals bonding at the CNT junctions where the outstanding phonon transport along the strong covalent bonding on the graphitic layer is largely impeded. In bulk materials, however, it has been extremely difficult to achieve covalently bonded junctions between CNTs. Here we report polymer composites consisting of sponge-like CNT structures whose junctions between CNTs are covalently bonded, resulting in a high thermal conductivity and a low Young's modulus, which are hard to achieve at the same time. The low modulus allows thermal interface material (TIM) to easily deform to make the surfaces of heat sink/source fully in contact, which is essential for TIM. Our facile scalable preparation process also makes our composite very attractive as TIM as well as provides insight to better utilize high thermal conductivity of CNTs.