The initiation of energetic materials by mechanical stimuli is a critical stage of their functioning, but remains poorly understood. Using atomic force microscopy (AFM) we explore the microscopic initiation behavior of four prototypical energetic materials: 3,4-dinitropyrazole, ϵ-CL-20, α-PETN and picric acid. Along with the various chemical structures, these energetic compounds cover a range of application types: a promising melt-cast explosive, the most powerful energetic compound in use, a widespread primary explosive, and a well-established nitroaromatic explosive from the early development of energetics. For the softest materials (picric acid and 3,4-dinitropyrazole), the surfaces were found to behave dynamically, quickly rearranging in response to mechanical deformation. The pit created by nanoscale friction stimulation on the surface of 3,4-dinitropyrazole doubled in volume upon aging for half an hour. Over the same time frame, a similar pit on the picric acid surface increased in volume by more than seven-fold. Remarkably, increased humidity was found to reduce the rate of surface rearrangement, potentially offering an origin for the desensitization of energetic materials when wetted. Finally, we identify an inverse correlation between the surface dynamics and mechanical sensitivity of our test energetic compounds. This strongly suggests that surface dynamics influence a material's ability to dissipate excess energy, acting as a buffer towards mechanical initiation.
Bibliographical noteFunding Information:
EKK and NVM acknowledge the Ministry of Science and Higher Education of the Russian Federation for a financial support of this work (project #075-15-2020-803 to Zelinsky Institute of Organic Chemistry). AAM received no funding for his contribution to this work. The authors are thankful to Konstantin Monogarov (Semenov Federal Research Center for Chemical Physic) for help with SPM experiments. Dr Igor Dalinger, Dr Ilya Kuchurov, Dr Leonid Fershtat (all from Zelinsky Institute of Organic Chemistry) are acknowledged for providing the substances for analysis.
© 2022 The Royal Society of Chemistry