High latent heat storage and high thermal conductive phase change materials using exfoliated graphite nanoplatelets

Using exfoliated graphite nanoplatelets (xGnP), paraffin/xGnP composite phase change materials (PCMs) were prepared by the stirring of xGnP in liquid paraffin for high electric conductivity, thermal conductivity and latent heat storage. xGnP of 1, 2, 3, 5 and 7wt% was added to pure paraffin at 75 C. Scanning electron microscopy (SEM) morphology showed uniform dispersion of xGnP in the paraffin wax. Good dispersion of xGnP in paraffin/xGnP composite PCMs led to high electric conductivity. The percolation threshold of paraffin/xGnP composite PCMs was between 1 and 2wt% in resistivity measurement. The thermal conductivity of paraffin/xGnP composite PCMs was increased as xGnP loading contents. Also, reproducibility of paraffin/xGnP composite PCMs as continuous PCMs was manifested in results of electric and thermal conductivity. Paraffin/xGnP composite PCMs showed two peaks in the heating curve by differential scanning calorimeter (DSC) measurement. The first phase change peak at around 35 degrees C is lower and corresponds to the solid-solid phase transition of the paraffin, and the second peak is high at around 55 degrees C, corresponding to the solid-liquid phase change. The latent heat of paraffin/xGnP composite PCMs did not decrease as loading xGnP contents to paraffin. xGnP can be considered as an effective heat-diffusion promoter to improve thermal conductivity of PCMs without reducing its latent heat storage capacity in paraffin wax. (c) 2008 Elsevier B.V. All rights reserved.