Transport Properties of Liquid Pentaerythritol Tetranitrate (PETN) from Molecular Dynamics Simulations

We have used molecular dynamics simulations to determine the transport properties of liquid pentaerythritol tetranitrate (PETN), an important energetic material. The density, ρ, self-diffusion coefficient, <i>D</i>, thermal conductivity, κ, and shear viscosity, μ, have been computed over pressures and temperatures relevant to the subshock regime (up to 1000 K and a few GPa), where PETN is known to melt prior to initiation. We find that the thermal conductivity κ(<i>P</i>, <i>T</i>) can be represented by a simple analytical function that fits the data points with very good accuracy, even beyond the subshock regime, up to 2000 K and 20 GPa. The self-diffusion coefficient, <i>D</i>, exhibits nonmonotonic behavior, with notably the temperature-independent prefactor decreasing by several orders of magnitude between 0 and 2 GPa before remaining nearly constant after, and the activation energy varying little in the subshock regime before increasing linearly beyond. Lastly, the viscosity, μ, is well described by Nahme's law, which is fitted to the MD results and allows us to predict μ(<i>P</i>, <i>T</i>) for temperatures and pressures corresponding to the subshock regime. These results can be used to model the response of PETN to low-velocity impacts, where the material melts prior to the first reactions, and thermal conduction and viscosity play a crucial role.