Enhanced thermal conductivity of phase change nanocomposite in solid and liquid state with various carbon nano inclusions

We report contrasting enhancement in the solid state and liquid state thermal conductivity of phase change nanocomposite seeded with various carbon nano inclusions. Phase change nanocomposites were prepared using n-Dodecanoic acid as the host matrix. Single-walled carbon nanohorns, multi-walled carbon nanotubes and few-layer graphene nanosheets were considered as the nano inclusions. Thermal conductivity measurements were carried out using a custom built transient hotwire technique. The thermal conductivity enhancement significantly depends on the shape and aspect ratio of the nano inclusions. Maximum thermal conductivity enhancement was obtained in the presence of graphene nanosheets as the nanofiller candidate followed by carbon nanotubes and carbon nanohorns. The thermal conductivity enhancement was significantly higher in the solid state than the liquid state of the material for all the nano composites. Thermal conductivity enhancement results were compared with the effective medium theory calculations and Yamada-Ota model calculations considering the role of interfacial thermal resistance between the nanomaterial and the surrounding host matrix. The model calculations show that that the interfacial thermal resistance significantly limits the thermal conductivity enhancement in the liquid state compared to the solid state. The model calculations also show that interfacial thermal resistance is an order of magnitude higher at the solid-liquid interface compared to that of solid-solid interface which leads to a contrasting thermal conductivity enhancement in liquid and solid state of the nanocomposites.