VACNT

Among graphite materials, carbon nanotubes (CNTs) are considered to be one of the most promising candidates for stable, highly thermally conductive heat dissipation films for high-power devices. CNTs have ultra-high axial thermal conductivity, and the axial thermal conductivity of well-structured single-walled CNTs can reach more than 6000 W/(m·K)....

• 
• 
• 
• 
• 
• 

Among graphite materials, carbon nanotubes (CNTs) are considered to be one of the most promising candidates for stable, highly thermally conductive heat dissipation films for high-power devices.

CNTs have ultra-high axial thermal conductivity, and the axial thermal conductivity of well-structured single-walled CNTs can reach more than 6000 W/(m·K).

Chen et al. used CNTs powder as a thermally conductive filler for polymers to improve thermal conductivity; however, the volume fraction of CNTs is small and the contact between random CNTs fillers is poor, which has limited improvement on the thermal conductivity of composite materials. CNTs buckypaper prepared by vacuum filtration of CNTs dispersion can show a thermal conductivity of more than 100 W/(m·K) in the plane direction. Therefore, the densely arranged CNTs structure is an ideal scaffold for transitioning CNTs from nanoscale to macroscale.

CNTs have strong sp2 hybridized carbon atoms and long phonon mean free path, and various CNT-based thermal conductive materials such as CNT/polymer composites and CNT arrays have been developed. Vertical carbon nanotube arrays (VACNTs) exhibit superior thermal conductivity in the thickness direction, and have both high thermal conductivity and high mechanical compliance. This helps to solve the thermal stress problem caused by the mismatch of thermal expansion coefficients between the two contacting surfaces, so VACNT is expected to become a candidate for high-performance thermal conductive materials in high-power devices.

Molecular dynamics simulations predict that the in-plane thermal conductivity of CNTs arrays is as low as 0.056 W/(m·K), which reduces the applicability of VACNT in high-power devices because high horizontal thermal conductivity is required when the size of the device and its corresponding heat source is reduced. The volume fraction of CNTs in VACNT is less than 5%, and the low volume fraction of CNTs in its composites has always been one of the key issues restricting its development.

In addition, many original crystal defects in CNTs arrays will also greatly limit their thermal conductivity. Due to the highly oriented structure of VACNT in the vertical direction, the interaction force between CNTs in the horizontal direction is relatively limited. The air gap in the middle causes its horizontal thermal conductivity and mechanical properties (bending strength, tensile strength, etc.) to deteriorate. Ultimately, VACNT is easily damaged by pressure in applications in high-power devices, or cannot completely fill the rough interface, thus failing to play its role in directional heat transfer.

• Previous: Carbon nanotube vertical arrays
• Next: Carbon nanotube vertical arrays VACNTs