Title: Effects of Branching and Polydispersity on Thermal Conductivity of Paraffin Waxes
Speaker: Maarten Boomstra (CCER)
Time: Sept. 23, 2021, 10:00–11:00
Location: Online (MS Teams)
Abstract: Paraffin waxes are promising phase change materials, abundantly available at very low cost and having large latent heat which can be used for thermal energy storage. However, when used in heat batteries, their low thermal conductivity prevents fast charging and discharging. Using fully atomistic molecular-dynamics simulations, we study the effects of polydispersity and branching on the thermal conductivity of paraffin waxes, above and below melting temperature. Both branching and polydispersity affect the density and especially the crystallinity of the produced samples. Branching has a pronounced effect on crystallisation caused by inhibited alignment of the backbones. The thermal conductivity (TC) has been simulated using the reverse non-equilibrium molecular-dynamics method, as well as the equilibrium Green-Kubo approach. Increased branching of eicosane chains results in decreasing thermal conductivity up to 30%, at the same time the polydispersity has a minor effect. Comparison to the available experiments show rather good agreement which validates the model details, force field in use and the calculation methods. For crystalline samples the size effects play an important role and the simulated TC values are very anisotropic. We show that at reasonable and comparable computational costs, the reverse non-equilibrium MD approach produces much more reliable results, as compared to the equilibrium Green-Kubo method. The suggested approach can definitely be used in future to model the eicosane-based nanocomposite materials with significantly enhanced thermal conductivity.