Thermal Interface Materials From Vertically Aligned Polymer Nanotube Arrays

A number of studies have reported enhancing the thermal conductivity of semi-crystalline polymers through mechanical stretching, but practical application of this process has proven difficult. Here we demonstrate the application of enhanced thermal conductivity in a purely amorphous polymer for a thermal interface material (TIM) without conductive fillers. Many polymer-based TIMs contain carbon fillers to enhance the thermal conductivity, however the TIMs reported herein are comprised solely of polymer nanotubes. The conjugated polymer polythiophene (Pth) is electropolymerized in nanotemplates to produce arrays of vertically aligned nanotubes, which adhere well to opposing substrates through van der Waals forces. We find that the total thermal resistances of the Pth-TIMs are a strong function of height with some dependence on bonding pressure, yet independent of applied pressure after bonding. Photoacoustic measurements show that the total thermal resistance of the TIMs ranges from 9.8 ± 3.8 to 155 ± 32 mm²-K/W depending on the array height and bonding pressure. Estimates of the component resistances indicate that the majority of the resistance is in the contact between the nanotube free tips and the opposing quartz substrate. These Pth-TIMs demonstrate that enhanced thermal conductivity polymers can be suitable for heat transfer materials without thermally conductive fillers.