Engineering the Microstructure and Morphology of Explosive Films via Control of Interfacial Energy

Abstract

Physical vapor deposition of organic explosives enables growth of polycrystalline films with a unique microstructure and morphology compared to the bulk material. This study demonstrates the ability to control crystal orientation and porosity in pentaerythritol tetranitrate films by varying the interfacial energy between the substrate and the vapor-deposited explosive. Variation in density, porosity, surface roughness, and optical properties is achieved in the explosive film, with significant implications for initiation sensitivity and detonation performance of the explosive material. Various surface science techniques, including angleresolved X-ray photoelectron spectroscopy and multiliquid contact angle analysis, are utilized to characterize interfacial characteristics between the substrate and explosive film. Optical microscopy and scanning electron microscopy of pentaerythritol tetranitrate surfaces and fracture cross sections illustrate the difference in morphology evolution and the microstructure achieved through surface energy modification. X-ray diffraction studies with the Tilt-A-Whirl three-dimensional pole figure rendering and texture analysis software suite reveal that high surface energy substrates result in a preferred (110) out-of-plane orientation of pentaerythritol tetranitrate crystallites and denser films. Low surface energy substrates create more randomly textured pentaerythritol tetranitrate and lead to nanoscale porosity and lower density films. This work furthers the scientific basis for interfacial engineering of polycrystalline organic explosive films through control of surface energy, enabling future study of dynamic and reactive detonative phenomena at the microscale. Results of this study also have potential applications to active pharmaceutical ingredients, stimuli-responsive polymer films, organic thin film transistors, and other areas.

Mode-Selective Vibrational Energy Transfer Dynamics in 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) Thin Films

“…Films on CaF 2 substrates were used for the experiments described below while those on BK-7 substrates were used for microstructure characterization. Though the morphology of the deposited film strongly depends upon the surface energy of the substrate, − the surface energy of clean CaF 2 is similar to typical oxides, , and we expect the final morphologies to be comparable between substrates. Microstructure characterization was performed by using scanning electron microscopy (SEM) to image the top surface and a fracture cross section of these films.…”

Selective Morphological and Polymorphic Control of CL-20 Thin Films Using Meniscus-Guided Coating

“…We attribute this to residual thermal stresses from the differences in the coefficient of thermal expansion between the silicon substrate and CL-20, as seen in pentaerythritol tetranitrate thin films. 29,30 The alleviation of this stress upon cooling produces submicron cracks, which can likely provide a location for hot spot formation, leading to lower sensitivity of the thin film. To produce thicker films without cracking, a higher solution concentration and lower operating temperatures may be used.…”

Mode-Selective Vibrational Energy Transfer Dynamics in 1,3,5-Trinitroperhydro-1,3,5-Triazine (RDX) Thin Films

“…Films on CaF2 substrates were used for the experiments described below while those on BK-7 substrates were used for microstructure characterization. Though the morphology of the deposited film strongly depends upon the surface energy of the substrate, [37][38][39] the surface energy of clean CaF2 is similar to typical oxides 40,41 and we expect the final morphologies to be comparable between substrates. Microstructure characterization was performed using scanning electron microscopy (SEM) to image the top surface and a fracture cross-section of films of each material.…”