Microfluidic Avenue\nto Manipulate Polycrystalline\nMaterials: A Case Study of 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-Hexaazaisowurtzitane

Polymorphic transformation is of\nparamount importance\nas it significantly\ninfluences the physical, chemical, and functional properties of materials,\nwith profound implications in fields ranging from advanced materials\nengineering to high-energy material science. However, there is difficulty\nin understanding transformation mechanisms, achieving precise control\nover transformation processes, and addressing the stability of polymorphs.\nThis work sets its sights on 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane\n(CL-20), a typical polycrystalline explosive, and innovatively embarks\non the development of a control strategy for polymorphic transformation\nfrom both mechanistic and experimental perspectives by microfluidics.\nWe delve into the microscopic transformation mechanisms from the α-form\nto the β-form and eventually to the ε-form, utilizing\nmolecular dynamics simulations incorporating thermodynamic and kinetic\nprinciples. To control these transitions, a custom-engineered coaxial\nmicromixer was developed, leading to the establishment of an advanced\nmicrofluidic system for polymorph control. The groundbreaking mechanism\nwas validated by scrutinizing the influence of microfluidic conditions\non the polymorphic transformation, facilitating a continuous and efficient\ntransition from α-CL-20 to ε-CL-20-PBX. Notably, thermal\ndecomposition tests provided further endorsement, confirming the superior\nstorage safety and reliability of ε-CL-20-PBX. The findings\noffer an unprecedented understanding of the polymorphic transformation\nof explosive materials and open new avenues in the manipulation of\npolycrystalline materials.