Superior thermal transport properties of vertically aligned carbon nanotubes tailored through mesoscale architectures

Abstract

Thermal transport properties play a critical role in the performance of lightweight foams used as shock-absorbing layers in helmets, sports gear, and electronic packaging. We report superior tailored thermal properties achieved at lightweight in vertically aligned carbon nanotube (VACNT) foams by introducing mesoscale hexagonally close-packed cylindrical architecture. We measure thermal diffusivity (α) using a laser flash technique and specific heat capacity (Cp) by differential scanning calorimetry at varying temperatures from 25 °C to 200 °C from which we determine the thermal conductivity and the thermal resistance as functions of temperature. The architected VACNTs exhibit similar α and Cp as non-architected VACNTs but exhibit higher intrinsic thermal conductivity (ki) and lower intrinsic thermal resistance (Ri) compared to the non-architected VACNTs. This improvement in ki and Ri arises due to the higher intrinsic density of VACNTs achieved by exploiting a synthesis size effect—the geometrically confined CVD synthesis which leads to higher vertical alignment and number density of CNTs. The effective thermal conductivity keff of VACNT foams follows a desirable sub-linear scaling with the density—which is tailored by the architecture—in contrast to the higher order scaling observed in other materials. The superior thermal transport properties of architected VACNTs enable lightweight protective materials for extreme engineering applications.