Thermal conductivity enhancement of phase change nanocomposites in solid and liquid state with nano carbon inclusions

Lauric acid based phase change nanocomposites with chemically functionalized graphene nanoplatelets (GnPs), multi-walled carbon nanotubes (MWCNTs) and single walled carbon nanohorns (SWCNHs) were prepared and its thermal conductivity was measured using transient hot wire method. We found that inclusion of graphene nanoplatelets increase the thermal conductivity of phase change nanocomposites by a factor of 2.3 at a loading of 1 vol %. We also show contrasting enhancements in thermal conductivity of such nanocomposites in the solid and liquid phase for the same loading of SWCNHs inclusions. Maximum thermal conductivity enhancement of SWCNHs inclusions in solid and liquid phase at 2 vol % is found to be ~37% and ~11% respectively. 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 considering the role of interfacial thermal resistance between the nanomaterial and the surrounding host matrix. The model calculations show 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.