Forests comprised of nominally vertically aligned carbon nanotubes (CNTs), having outstanding thermal and mechanical properties, are excellent candidates for thermal interface materials (TIMs). However, the thermal performance of CNT forest TIMs has been limited by the presence of high thermal contact resistances at the CNT tip interface. The high thermal contact resistance at the CNT tip interface stems from two sources: (1) the relatively weak van der Waals type bonding, which impedes phonon transport, and (2) low contact area. In this work we will show that common solvents, such as water, can be applied to the CNT forest to increase the contact area and reduce the contact resistance by an average of 75%. Specifically, there are two likely mechanisms that can increase the contact area when a CNT forest is wet with a fluid and compressed in an interface. The first is relaxing the van der Waals interactions between contacting CNTs within the forest, consequently decreasing the stiffness of the forest and allowing it to better conform to the opposing surface. The second is the pulling of CNT tips through capillary interactions into contact with the opposing surface as the solvent evaporates. By measuring the thermal resistance of CNT TIMs before and after soaking in variety of solvents the capacity of each mechanism for reducing the contact resistance is explored.
Effects of van der Waals interactions on the phonon transport properties of tetradymite compounds
