Filler dimensionality effect on the performance of paraffin-based phase change materials

Hypothesis: Phase change materials have the potential for use in high-density thermal energy storage. However, their low thermal conductivity and the need for shape stabilization restrict their performances and implementation in various fields. The inclusion of thermally conductive nanomaterial as a single or hybrid filling is expected to form 3D network that enhances the thermal performances of phase change materials. The encapsulation of the colloidal composites in a polymer matrix stabilizes the phase change material. Experiments: A paraffin matrix was loaded with carbon-based fillers of various dimensionalities, namely, 1D-carbon nanotubes, 2D-graphene nanoplatelets, and 3D-graphite flakes. The thermal conductivity of the colloidal composite was measured by transient plane source and the latent heat capacity by differential scanning calorimetry techniques. Modeling the thermal conductivity by the effective medium approach predicts the experimental results. Findings: The thermal conductivity of the phase change material loaded with fillers is enhanced from 0.2 to 11 W (m K)^-1 (×55) compared with a filler-free paraffin matrix. We attribute this enhancement to the synergetic effect of the hybrid fillers (8 vol% graphite flakes and 12 vol% graphene nanoplatelets) and consequent compression (25 bar) of the colloidal composite. Moreover, the obtained phase change material is completely stable during charging and discharging cycles.