Fabrication of hierarchically hollow RDX microspheres by quasi-emulsion solvent diffusion for improved safety and combustion performance

Hierarchically hollow structures exhibit significant potential in energetic materials owing to their ability to enhance combustion efficiency while reducing mechanical sensitivity. However, the controlled fabrication of such structures in energetic crystals remains a major challenge. In this study, hierarchically hollow RDX microspheres (HH-RDX) were fabricated via a quasi-emulsion solvent diffusion method, and the effects of solute concentration, polyvinyl alcohol (PVA) content, and stirring rate on their morphology and particle size distribution were systematically investigated. The formation mechanism of HH-RDX and its structure–property relationships were clarified through combined structural characterization, thermal analysis, combustion and sensitivity testing, and molecular dynamics simulations. HH-RDX retained the crystal phase and molecular structure of raw RDX, while exhibiting lower activation energy, improved combustion performance, and reduced impact sensitivity. Compared with raw RDX, HH-RDX exhibited a larger peak flame area (294.55 vs. 84.92 mm²) and a shorter combustion duration (1072 vs. 1330 ms). The H₅₀ value increased from 20.22 cm to 31.74 cm, indicating that the impact sensitivity was significantly reduced. Molecular dynamics simulations revealed that the initial solvent exchange was dominated by the diffusion of water molecules into the droplets, which promoted the interfacial enrichment and preferential deposition of RDX, thereby driving shell formation and the retention of the hollow structure. This work provides an effective strategy for the controlled fabrication of HH-RDX with improved safety and combustion performance.