Beyond Percolation: Graphene-Enabled Network Reinforcement Enhances Thermal Transport in Paraffin Phase-Change...

Paraffin phase-change materials store thermal energy through latent heat, making them attractive for thermal management and energy storage applications. However, their low thermal conductivity ( $\kappa$ ) limits heat transfer rates and restricts rapid charging-discharging cycles. Achieving substantial $\kappa$ enhancements at low filler loadings, without degrading phase-change enthalpy, remains a critical challenge. Here we show that expanded-graphite (EG) worms and graphene nanoplatelets (GNPs) act synergistically in paraffin composites at low loadings ( $\le 5\mathrm{wt}\%$ ). At $5\mathrm{wt}\%$ filler, 1:1 EG-GNP hybrids raise $\kappa$ from 0.25 to $2.7W{m}^{-1}{K}^{-1}$ , outperforming single-filler composites while preserving the melting window and latent heat. Microscopy suggests that GNPs suppress EG breakup during processing and reinforce surviving worms, and micro-computed tomography (microCT) reveals a percolating EG backbone that spans the composite. To connect microstructure to thermal transport, a microCT-informed, resolution-aware 3D modeling framework was developed. Within this framework, a graphene-enabled network-reinforcement mechanism is proposed: graphene nanoplatelet reinforcement of the EG network effectively enhances intraworm connectivity and redistributes heat flux at local constrictions. This mechanism surpasses predictions based solely on percolation geometry or filler fraction and establishes a quantitative design principle for high-performance hybrid phase-change composites.