Graphene Nanoplatelet Distribution Governs Thermal Conductivity and Stability of Paraffin-Based PCMs

Materials for heat storage are important to fully utilize renewable energy sources and to realize a constant, on-demand supply. Organic phase change materials (PCMs) can play a crucial role in heat storage, as they have many advantages; however, their widespread commercial adoption is hindered by their low thermal conductivity and lack of cyclic stability. To enhance performance, highly thermally conductive fillers such as graphene nanoplatelets (GNPs) have been used; however, the role of the filler network has not been investigated. Here, we present, from a colloidal perspective, an in-depth study of GNP networks in paraffin PCMs. We investigate how GNP size, aspect ratio, and network topology determine thermal conductivity and cyclic stability of the composite. Our results show that the best-performing GNP network is random, with an optimized GNP aspect ratio. Filler fractions should be such that overlap between GNPs is guaranteed, which prevents leakage of paraffin from the composite, ensuring cyclic stability. These results not only contribute valuable insights into the design of new PCM composites but also emphasize the significance of considering filler geometry and network topology alongside filler type and fraction for optimizing thermal performance and cyclic stability.