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.

The CCER seminars are aimed at researchers interested in computational approaches to (energy) research. The seminar is small-scale, typically 15 participants, and interactive, offering lots of room for discussion. If you would like to attend, just This email address is being protected from spambots. You need JavaScript enabled to view it. so as to receive the MS Teams meeting link.

Title: A Reactive Force Field for Large Scale Simulations of Metal Halide Perovskites.

Speaker: Mike Pols (CCER)
Time: April 08, 2021, 10:00–11:00
Location: Online (MS Teams)

Abstract: Perovskite solar cells have amassed great attention over the recent years, mainly because of the high solar cell efficiencies that they result in. Nevertheless, the practical use of this type of solar cell is limited by their lacking long-term stability. Over the years many computational studies have been done to understand this complex material and aid in the development of stable perovskite solar cells. The bulk of these investigations were done using methods based on quantum mechanics (QM). However, the computational cost of QM methods is high, severely limiting the length and time scales of the systems that can be investigated. Molecular dynamics (MD) simulations have been successfully applied to simulate larger material systems and at longer time scales by making use of classical force fields (CFF). Nonetheless, the predefined connectivity in CFF makes them unsuited for the simulation of chemical reactions. A reactive force field (ReaxFF) is an extension to CFF by including a dynamic bond order that is calculated from the interatomic distances and allows for the simulation of bond breaking and formation. In this presentation I will outline my recent efforts towards the creation of the first ReaxFF description for metal halide perovskites and elaborate on the perovskite stability on the basis of simulations done with ReaxFF.

The CCER seminars are aimed at researchers interested in computational approaches to (energy) research. The seminar is small-scale, typically 15 participants, and interactive, offering lots of room for discussion. If you would like to attend, just This email address is being protected from spambots. You need JavaScript enabled to view it. so as to receive the MS Teams meeting link.

Title: Modeling novel thermal transport phenomena in semiconductor nanowires.

Speaker: Subash Gireesan (CCER)
Time: March 11, 2021, 10:00–11:00
Location: Online (MS Teams)

Abstract: Transport of heat, i.e. thermal energy, plays an important role in our daily lives. Ranging from regulating the temperature of our body to cooling down our electronic devices, the importance of heat transport is not often valued as we go about with our lives. Efficient management of heat is crucial in designing devices like internal combustion engines, electronics, space crafts, solar collectors, gas turbines and radiators. In some applications, excess heat has to be removed and in others, it has to be added. The challenge for the engineers and scientists is to design systems in such a way that the usage or dissipation of heat can be optimized. In the last few decades, manipulating and controlling thermal transport at the nanoscale has garnered wide interest. This is mainly motivated by the need for understanding and improving the efficiency of systems and devices for various technological applications like thermal management of microelectronics, thermoelectric energy conversion, thermal energy storage and thermal rectification. Probing thermal transport in nanoscale materials like semiconductor nanowires has revealed novel transport behavior like room-temperature ballistic transport of phonons. For a better understanding of the origin of novel thermal transport phenomena in nanomaterials, new models and theories are required. In this talk, I will present some of the main results from our work on modeling thermal transport in semiconductor nanowires. I will briefly talk about the models that we developed to better understand novel results from thermal transport measurements on GaP nanowires.

The CCER seminars are aimed at researchers interested in computational approaches to (energy) research. The seminar is small-scale, typically 15 participants, and interactive, offering lots of room for discussion. If you would like to attend, just This email address is being protected from spambots. You need JavaScript enabled to view it. so as to receive the MS Teams meeting link.