Enhancement of through-thickness thermal conductivity in adhesively bonded joints using aligned carbon nanotubes

A concept of incorporating aligned multi-walled carbon nanotubes (MWCNTs) in the adhesive layer has been demonstrated to enhance the through-thickness thermal conductivity in the adhesively bonded joints. Both numerical and experimental studies were performed to determine key components in improving the through-thickness thermal conductivity and to realize the improvement in an adhesively-jointed system. The numerical analysis indicated that the key components to improve the through-thickness thermal conductivity in the adhesive joints are using highly conductive vertically aligned nanotubes as well as the thermal conductivity and the size of a transition zone between the nanotube ends and surrounding matrix materials in the form of either the adhesive or adherends. Therefore, the thermal contact of the conductive phase (the MWNT in this case) with the adherent surfaces is essential to achieve the desirable through-thickness thermal conductivity in joints. This theoretical observation was demonstrated experimentally by using conductive graphite facesheets as adherends and the polymer adhesive layer with the aligned MWCNTs. To ensure the ends of the MWCNTs make thermal contact with the adherent surfaces, the surface of the adhesive with the MWCNTs were plasma-etched and coated with thin Au layer, along with the surface of the graphite facesheet coated with thin Au–Pd layer. The measured value of the through-thickness thermal conductivity of the modified adhesive joint with the MWNCT was over 250 W/m K, which superseded the thermal conductivity of neat adhesive joint by several order of magnitudes. Thus the study demonstrates a new approach as well as opportunities of much needed thermal property tailoring in structural joints.