Examining the combined effect of physical and chemical sensitizers in liquid explosives

Increasing the sensitivity of a liquid explosive lowers the amount of external energy required to trigger its detonation. Sensitivity can be raised physically, by adding tiny hollow glass spheres that collapse during detonation and create microscopic hot spots where the reaction is faster, or chemically, by adding amine to lower the activation energy of the decomposition reaction.

These methods are typically used and studied separately, but Mochalova et al. wanted to investigate their combined effect. The authors explored the detonation of nitromethane, a classic detonation model system, after adding different compositions of an amine and hollow microspheres.

They found that amine alone achieved the best sensitization of the liquid explosive. With a few microspheres, the amine continued to work well. However, as more microspheres were added, the effect of the amine weakened until it almost vanished.

A high-speed camera showed that as the number of microspheres increases, the hot spots around them expand and merge into a connected network. After passing this merging threshold, most of the liquid reacts inside the hot spots. This leaves little material for the amine to accelerate, reducing its contribution.

The results will help tune the sensitivity of liquid explosives using both chemical and physical sensitizers.

“A chemical sensitizer is worth adding only while the material remains relatively homogeneous. Beyond the threshold, one should work with the size and distribution of the physical inclusions instead,” said author Valentina Mochalova. “This is useful both for those who develop energetic materials and for those concerned with their safety, since the same physics governs unintended initiation.”

Next, the authors will explore different sizes and materials of physical sensitizers to see if the same merging threshold exists in other systems.

Source: “Combined effect of microballoons and diethylenetriamine on the detonation of nitromethane,” Valentina Mochalova, Alexander Utkin, Mikhail Shakula, Vladimir Lavrov, Andrey Savchenko, Vasilii Sosikov, Sergey Torunov, Daniil Rapota, Sergey Koldunov, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0351017 .