Imparting Switchable Impact Sensitivity to Workhorse Explosives

Abstract

Explosives underpin applications ranging from military technologies to mining and construction. Safety risks during material transport are often mitigated using formulation strategies, such as polymer bonding, that reduce sensitivity; however, reduced sensitivity can result in incomplete detonation, compromising performance. These competing demands motivate the development of switchable energetic materials whose sensitivity can be externally activated to enable truly on-demand detonation. We demonstrate that novel spiropyran compounds (1-SP and 2-SP), designed to function as electrostatic molecular switches, enable the modulation of explosive sensitivity using light as the sole external stimulus, forming a zwitterionic merocyanine (MC). Pure HMX crystals were shown to be less sensitive to impact than 5 wt % 1-SP and 1 wt % 2-SP coated crystals following UV irradiation, as the impact sensitivity, E50, decreased from 2.7 ± 0.1 J to 2.2 ± 0.1 J for 1-MC and 2.3 ± 0.1 J for 2-MC. Furthermore, these compounds are seamlessly integrated into the research formulation, PBXN-110. Impact sensitivity decreased to 3.8 ± 0.1 J for 1 wt % 1-SP and 4.7 ± 0.1 J for 1 wt % 2-SP, relative to pure HMX (2.7 ± 0.1 J) when encased within the PBXN-110. When exposed to UV light, the 1 wt % 1-MC material exhibits an E50 of 3.2 ± 0.1 J and 1 wt % 2-MC of 3.8 ± 0.1 J, demonstrating the ability of the merocyanine compounds to affect sensitivity even within a polymer matrix. Integration of these compounds into established desensitization strategies provides an unprecedented platform for dynamically controlling impact sensitivity without compromising performance.