Thermal Conductivities of Uniform and Random Sulfur Crosslinking in Polybutadiene by Molecular Dynamic Simulation

Thermal conductivities of polybutadiene crosslinked with sulfur as a function of the heat flux autocorrelation function by using an equilibrium molecular dynamic (EMD) simulation were investigated. The Green-Kubo method was used to calculate thermal conductivities. All simulations were performed by applying the LAMMPS software (version 3 Mar 2020) package. The united-atom force field (OPLS-UA) from the Moltemplate software (version 2.20.3) was applied in the simulations. The influence of uniform and random distributions of sulfur in polybutadiene on the final value of thermal conductivities was studied by polymeric model structures with similar and variable degrees of crosslinking. The results showed that for identical degrees of crosslinking, the distribution of crosslinkers in the polymeric model structures significantly influenced the final value of thermal conductivity. Moreover, the influence of the crosslinking degree on the final value of thermal conductivity was studied by considering polymeric model structures with different degrees of crosslinking. The results demonstrate that by having a random distribution of sulfur, the thermal conductivity will be enhanced. However, by increasing the degree of crosslinking to the higher percentage in random crosslinked model structures, the value of thermal conductivity drops significantly due to possible higher crystallization of the model structures, which decrease the degree of freedom for phonon contributions.

Automated summary

The thermal conductivities of sulfur crosslinked polybutadiene were studied using equilibrium molecular dynamic (EMD) simulations, focusing on the relationship between thermal conductivities and heat flux autocorrelation functions. The Green-Kubo method was applied to calculate thermal conductivities, and LAMMPS software and the OPLS-UA force field from Moltemplate software were used in the simulations. The influence of uniform and random distributions of sulfur on thermal conductivities was investigated, as well as the effect of crosslinking degree. The results showed that the distribution of crosslinkers significantly affected the thermal conductivity, and a random distribution of sulfur enhanced the thermal conductivity.