Molecular dynamics simulation of TNT/PYRN cocrystal PBXs

Abstract

Context: The ternary eutectic system comprising trinitrotoluene (TNT) and pyranidine (PYRN) exhibits potential as a moderate-energy explosive compound characterized by reduced sensitivity. Recently, this composition can be a suitable alternative to TNT in the development of low-vulnerability explosive formulations, thus providing a promising alternative for future applications in the field of energetic materials. However, the changes in the structure and properties of eutectic explosives and their intrinsic causes for these changes have been rarely explored. Here, we construct a theoretical model of the TNT/PYRN eutectic system and integrates a diverse array of polymer additives, including butadiene rubber (BR), ethylene-vinyl acetate copolymer (EVA), polyethylene glycol (PEG), fluorinated polymer (F2603), and polyvinylidene fluoride (PVDF), into five distinct cleavage planes ((1 0 0), (0 1 0), (0 1 - 1), (1 0 0), and (1 0 - 1)) within the eutectic matrix. We found that the synthesis of polymer-bonded explosives (PBXs) is achieved through the integration of the aforementioned polymers into the TNT/PYRN eutectic system. This investigation elucidated the influence of various polymer matrices on the structural integrity, critical bond distances for initiation, mechanical attributes, and detonative behavior of the resultant PBXs. Within the corpus of five PBX models examined, the TNT/PYRN/F2603 configuration showed the supremum in binding energetics and the infimum in critical bond lengths, which portends superior stability, interfacial harmony, and a minimized propensity for unintended initiation. Furthermore, the TNT/PYRN/F2603 system was delineated by its enhanced capability for explosive initiation. Note importantly that the TNT/PYRN/F2603 model exhibited pre-eminence in its aggregate performance metrics, corroborating the hypothesis that F2603 constitutes a preferential binder candidate for PBX formulations predicated on the TNT/PYRN eutectic composite.

Methods: Utilizing the Materials Studio computational platform, the physicochemical attributes of the TNT/PYRN eutectic-based polymer-bonded explosives (PBXs) were anticipated via molecular dynamics (MD) simulations. The MD protocol was executed with a temporal increment of 1 fs, encompassing an aggregate simulation span of 2 ns. An isothermal-isobaric (NPT) thermodynamic ensemble was employed for the duration of the 2 ns MD trajectory. The COMPASS empirical force field was utilized to model interatomic interactions, and the thermal parameter was maintained at a constant 295 K throughout the simulation campaign.

Keywords: Binding energy; Mechanical properties; Molecular dynamics (MD) simulation; Polymer-bonded explosives (PBXs); TNT/PYRN eutectic explosive; Trigger bond length.