Strain Engineering for Thermal Conductivity of SWCNT Forests

TL;DR

This study uses molecular dynamics simulations to explore how mechanical compression affects the thermal conductivity of SWCNT forests, revealing a linear increase before buckling and a sharp decrease afterward due to structural changes.

Contribution

It provides new insights into the relationship between mechanical compression, buckling, and thermal conductivity in SWCNT forests, highlighting the role of phonon modes and inter-tube interactions.

Findings

Thermal conductivity increases linearly with compression before buckling.

Post-buckling, thermal conductivity decreases rapidly due to structural changes.

Inter-tube van der Waals interactions are strengthened by compression before buckling.

Abstract

We perform classical molecular dynamics simulations to investigate the mechanical compression effect on the thermal conductivity of the single-walled carbon nanotube (SWCNT) forest, in which SWCNTs are closely aligned and parallel with each other. We find that the thermal conductivity can be linearly enhanced by increasing compression before the buckling of SWCNT forests, but the thermal conductivity decreases quickly with further increasing compression after the forest is buckled. Our phonon mode analysis reveals that, before buckling, the smoothness of the inter-tube interface is maintained during compression, and the inter-tube van der Waals interaction is strengthened by the compression. Consequently, the twisting-like mode (good heat carrier) is well preserved and its group velocity is increased by increasing compression, resulting in the enhancement of the thermal conductivity. The buckling phenomenon changes the circular cross section of the SWCNT into ellipse, which causes effective roughness at the inter-tube interface for the twisting motion. As a result, in ellipse SWCNTs, the radial breathing mode (poor heat carrier) becomes the most favorable motion instead of the twisting-like mode, leading to the quick decrease of the thermal conductivity with further increasing compression after buckling.