Thermal Conductivity of Single-Wall and Multi-Wall Carbon Nanotubes

One-dimensional materials, such as nanotubes, and their composites attract interest due to their potential use in applications as well as model systems for understanding low-dimensional physics. There is a need for detailed measurements of the specific heat ($c_p$) and thermal conductivity ($\kappa$) in order to guide theoretical efforts. This talk presents $c_p$ and $\kappa$ using an ac-calorimetric technique for single-wall (SW) and multi-wall (MW) carbon nanotubes (CNT) in a composite sample+cell arrangement. From $300$ to $400$~K, $c_p$ exhibits a linear behavior for both nanotubes. However, $\kappa$ for MWCNT and SWCNT with the heat flow perpendicular to the nanotube long-axis is bulk-like in behavior until $\approx 370$~K, thereafter decreasing with increasing temperature, indicating the onset of phonon-phonon scattering. For samples where the heat flow is parallel to the nanotube long-axis, $\kappa$ for the MWCNT sample is consistent with ballistic phonon transport.