Thermal conductivity enhancement of carbon@ carbon nanotube arrays and bonded carbon nanotube network

Abstract

Carbon nanotubes (CNTs) are long considered as a promising material for thermal applications. However, problems such as low volume CNT fraction abhorrent to practical applications have been raising the demand for novel architecture of this material. Here we demonstrate two fabrication methods, in which a self-assembly method for fabricating covalent-bonded CNT network (3D CNT) and another method for covalent-bonded C to CNTs (C@CNT) network, and presented both as a potential method to enhance thermal conductivity of CNT arrays. We utilized pulsed photothermal reflectance technique and using new four-layer heat conduction model based on the transmission-line theory to measure thermal conductivity of the samples. The 3D CNT with thermal conductivity of 21 W mK−1 and C@CNT with thermal conductivity of 26 W mK−1 turn out to be an excellent candidate for thermal interface material as the thermal conductivity increased by 40% and 70% respectively as compared to conventional CNT arrays. The improvement is attributed to the efficient thermal routines constructed between CNTs and secondary CNTs in 3D CNT and between C layer and CNTs in C@CNT. The other factor to improve thermal conductivity of the samples is decreasing air volume fraction in CNT arrays. Our fabrication methods provide a simple method but effective way to fabricate 3D CNT and C@CNT and extend the possibility of CNTs towards TIM application.

Enhancement of thermal interface material properties using carbon nanotubes through simple electrophoretic deposition method

“…The CNTs were scattered and formed less uniform deposition with slightly packed structures. Therefore, small increments were obtained on weight deposited CNTs . Thus, the applied voltage of 175 V was moderate for performing optimum deposition of CNTs with good quality and adhesion.…”

“…Therefore, nanomaterials with good thermal properties are predominately selected by most researchers because of their capability to perform at nanoscale dimensions . The most prominent nanomaterials are carbon nanotubes (CNTs) and graphene because of their excellent thermal properties, especially in conducting heat (more than 3000 W/m∙K) and internal resistance (1 × 10 −6 m 2 ∙K/W) . CNTs are stable in carbon atom hexagonal structures, which are commonly produced in growth methods, such as chemical vapor deposition (CVD) .…”

“…One of the biggest challenges for CNT applications in TIM is the difficulty of combining CNTs with other materials and their proper positioning on the substrate of TIM packaging known as the heat spreader. Many conventional methods, including growth methods, such as CVD and various coating methods (spin coating, electrophoretic, electroplating, and screen printing) are used to place materials on the heat spreader . Growth methods, such as CVD, are beneficial for providing good material and mechanical contacts with the surface.…”

“…Growth methods, such as CVD, are beneficial for providing good material and mechanical contacts with the surface. However, the limitations lie in material purity, CNT density, and high operation temperature, affecting the substrates for electronic applications . The purity and density of CNTs are easy to control in coating methods.…”

Hybrid carbon thermal interface materials for thermoelectric generator devices

“…However, fabricating an efficient TIM with a CNT filler is difficult because of the low filling fraction, low degree of dispersion and high thermal interface resistance of CNTs 16 , 17 . To reduce the high thermal resistance at the interface of CNT–CNT or CNT-contact materials, various approaches have been recently reported, such as carbon-based bonding 18 , 19 , metal-based bonding 20 – 24 , infiltration with phase change materials (PCMs) or epoxy 7 , 25 , polymer coating 26 and chemical functionalization 27 – 29 .…”