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

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 (a) using a laser flash technique and specific heat capacity (Cp) by differential scanning calorimetry at varying temperatures from 25 degrees C to 200 degrees C from which we determine the thermal conductivity and the thermal resistance as functions of temperature. The architected VACNTs exhibit similar a 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 kef f 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.