Interfacial stability effect of PDA@PVDF dual-coating on CL-20: Synergistically suppressed polymorphic transition and solubility

Abstract

Hexanitrohexaazaisowurtzitane (CL-20) is a high-energy explosive widely used in composite explosives and propellants, but its application is severely limited by thermally induced ε-to-γ polymorphic transition and high solubility in nitrate ester solvents. The transition reduces energy density and increasing sensitivity, and the solubility causes dissolution-recrystallization defects (e.g., voids, compositional inhomogeneities) during long-term storage. To address these issues while preserving its high energetic performance, this study developed a polydopamine@polyvinylidene fluoride (PDA@PVDF) dual-coating strategy, fabricating CL-20 composite particles with a core-shell structure. In-situ X-ray diffraction (XRD) results confirmed that the ε-to-γ phase transition temperature of CL-20 increased from 110 °C (pristine CL-20) to 140 °C. Meanwhile, the CL-20@PDA@9%PVDF sample exhibited the lowest solubility and the best solvent resistance, and the solubility of CL-20 in nitrate ester solvents was drastically reduced from 0.229 g/100 g to 0.026 g/100 g, an 88.6% decrease, effectively enhancing its structural and solvent resistance stability. For energetic performance, when mixed with aluminum powder at a 7:3 mass ratio, the CL-20@PDA@9%PVDF/Al composite achieved a combustion heat of 8275 J/g, 8.7% higher than that of the unmodified Al/CL-20 system (7611 J/g). Combustion pressure tests showed that although the modified system exhibited slightly lower initial peak pressure and pressure rise rate due to dilute CL-20 content from inert coatings, it presented a unique "delayed enhancement" effect, with pressure gradually surpassing and ultimately exceeding that of the unmodified system in the middle and late combustion stages, enabling more sustained high-pressure output. This work realizes the synergistic optimization of CL-20’s polymorphic/solvent stability and energetic performance, providing a feasible and scalable approach for the practical application of CL-20 in advanced energetic systems.