Constructing solid microspheres of CL-20/MTNP cocrystal via droplet microfluidics for improved performance

Abstract

The design and fabrication of materials with hierarchical structures have drawn great attention due to the potential for significantly enhancing their functions. Herein, the droplet microfluidics technology was employed to construct the binder-free microspheres of a CL-20 (8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane)/MTNP (1-methyl-3,4,5-trinitropyrazole) cocrystal, which is an energetic cocrystal with excellent comprehensive performance. The effects of dispersed phase concentrations, continuous phase flow rates and surfactant concentrations in the continuous phase on the morphology and size of microspheres were studied via experiments and computational fluid dynamics (CFD) simulations. The optimal parameters for obtaining solid cocrystal microspheres (D₅₀ = 54.36 μm) with a uniform particle size and high sphericity were determined by scanning electron microscopy, infrared spectroscopy, laser particle analysis and laser scanning confocal microscopy analyses. The dispersed concentrations mainly affect the crystallization process, while surfactant concentrations in the continuous phase significantly influence the droplet formation process. The as-prepared microspheres have a high true density (1.8125 g cm⁻³) and purity (99.6%), good flowability with an angle of repose of 22.2°, and improved mechanical sensitivity close to that of raw MTNP. This work not only presents a simple and convenient microfluidic method for fabricating solid microspheres of energetic cocrystals with enhanced performance but also provides insights into the droplet formation process, promoting the further application of droplet microfluidics technology in the energetic materials field.