Molecular dynamics study on the relationships of modeling, structural and energy properties with sensitivity for RDX-based PBXs

In this paper, a primary model is established for MD (molecular dynamics) simulation for the PBXs (polymer-bonded explosives) with RDX (cyclotrimethylene trinitramine) as base explosive and PS as polymer binder. A series of results from the MD simulation are compared between two PBX models, which are represented by PBX1 and PBX2, respectively, including one PS molecular chain having 46 repeating units and two PS molecular chains with each having 23 repeating units. It has been found that their structural, interaction energy and mechanical properties are basically consistent between the two models. A systematic MD study for the PBX2 is performed under NPT conditions at five different temperatures, i.e., 195 K, 245 K, 295 K, 345 K, and 395 K. We have found that with the temperature increase, the maximum bond length (L (max)) of RDX N-N trigger bond increases, and the interaction energy (E (N-N)) between two N atoms of the N-N trigger bond and the cohesive energy density (CED) decrease. These phenomena agree with the experimental fact that the PBX becomes more sensitive as the temperature increases. Therefore, we propose to use the maximum bond length L (max) of the trigger bond of the easily decomposed and exploded component and the interaction energy E (N-N) of the two relevant atoms as theoretical criteria to judge or predict the relative degree of heat and impact sensitivity for the energetic composites such as PBXs and solid propellants.