Modelling water diffusion in plasticizers: development and optimization of a force field for 2,4-dinitroethylbenzene and 2,4,6-trinitroethylbenzene.

A classical all-atom force field has been developed for 2,4,6-trinitroethylbenzene and 2,4-dinitroethylbenzene and applied in molecular dynamics simulations of the two pure and two mixed plasticizer systems. Bonding parameters and partial charges were derived through electronic and geometry optimization of the single molecules. The other required parameters were derived from values already available in the literature for generic nitro aromatic compounds, which were adjusted to reproduce to a high level of accuracy the densities of 2,4-dinitroethylbenzene, 2,4,6-trinitroethylbenzene and the energetic plasticizers K10 and R8002. This force field has been applied to both K10 and R8002, which when used as plasticizers form an energetic binder with nitrocellulose. Nitrocellulose decomposes in storage, under varying conditions, but in particular where it may become increasingly dry. Following the derivation of the force field, we have therefore applied it to calculate water diffusion coefficients for each of the different materials at 298 K and 338 K, thereby providing a starting point for understanding water behaviour in a nitrocellulose binder.