Insights into Periodically Noncovalent Interaction-Induced Decrease in Thermal Conductivity of Carbon Nanotubes from Coherent and Incoherent Phonon Transport

Noncovalent interaction-induced deformation is one of the most promising methods for tuning thermal conductivity because it does not alter the atomic structure and thus causes reversible changes in properties. Taking carbon nanotube (CNT) as a model, we found that by applying periodic van der Waals (vdW) forces based on C60 encapsulation, the thermal conductivity can be reduced by 58.64% compared with that without vdW force and by 34.09% compared with that with uniform vdW interactions (150 K). Physical insights are gained from both coherent and incoherent phonon transport. Due to the periodic distribution of Mises stress and Gaussian curvature in CNT with periodic vdW forces, the coherent interfaces between CNT parts with positive and zero Gaussian curvatures are formed, which help satisfy the Bragg condition. The phonon group velocities are found to decrease due to the reduced elastic modulus, Bragg scattering, and phonon localization. Additionally, the coherent interfaces induce phonon interface scattering and thus result in a further reduction in phonon relaxation time. With the magnitude of vdW interaction increasing, the thermal conductivity of CNT experiences a decrease followed by an increase. It is attributed to the dominant role of the coherent phonon transport. The periodically noncovalent interaction provides the possibility to control thermal conductivity without changing the pristine structure.