Identifying and understanding the factors that influence handling sensitivity is critical for screening new energetic materials. Impact sensitivity is typically dictated by the interplay between multiple chemical and physical effects over disparate length scales, from the energetic functional groups in a molecule to mesoscale structure and defects. Specifically, sensitivity has been suggested to be governed by multiple factors, from intrinsic molecular properties such as bond dissociation energy, oxygen balance, and the electrostatic potential of reactive functional groups, to larger scale effects, such as crystal structure and hot spot formation. Due to these various competing effects, a general theory of sensitivity in explosives has not been proposed. In order to gain insight into the molecular properties that govern sensitivity, we have been examining explosives molecules and evaluating – both experimentally and theoretically – how changes to the molecular structure affect thermodynamic properties and crystal packing, and potentially influence mechanical sensitivity. Specifically, we have prepared derivatives of pentaerythritol tetranitrate (PETN), a common initiating explosive, by replacing one of the –CH2ONO2 substituents with hydrogen, amino, and methyl groups attached to the central carbon atom. With this molecular framework, we have evaluated how small changes to the structure of the molecule influence qualities such as oxygen balance, heat of formation, heat capacity, compressibility, crystal packing, and hydrogen bonding, through techniques such as differential scanning calorimetry, x-ray crystallography, and atomistic simulation. Small-scale sensitivity testing has shown consistent differences in handling sensitivity between the derivatives. Reactive molecular dynamics simulations indicate that very similar chemistry occurs in early reactions at the nitrate ester functional group. However, X-ray crystallographic analyses found significant differences in hydrogen bonding and crystal packing, suggesting that the variation in sensitivity among the PETN-based molecules are due to larger scale effects.

Examining the effects of structural modifications on explosive sensitivity

255th National Meeting (2018)

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