Microfluidic preparation of size-controlled ultrafine-HNS for laser ignition with shortened delay time

The poor sensitivity of relatively insensitive explosives to near-infrared light limits their potential applications in laser ignition technology. In addition to introducing external sensitizers, regulating the aggregation form of explosive molecules to control their laser ignition performance is another key approach that deserves particular attention. Herein, using hexanitrostilbene (HNS) as the model, the influence of crystal size on its light response characteristics and laser ignition performance was studied. A series of HNS particles with well-controlled sizes ranging from 140 nm to several micrometers were successfully prepared via a microfluidics-based recrystallization method. The as-prepared samples retained the same crystal structure and excellent thermal stability as raw HNS, while exhibiting distinct size-dependent physicochemical properties. Notably, the reduction in crystal size led to enhanced light absorption and altered pyrolysis behavior, both of which are favorable for photothermal energy conversion. Importantly, this size effect remains effective even in the presence of photosensitizers, indicating its intrinsic contribution to light–matter interaction. As a result, the laser ignition delay time of HNS/carbon composites is significantly reduced from 52 ms to 18 ms with decreasing particle size. This work not only demonstrates an efficient, continuous, and safe technical route for the preparation of ultrafine HNS, but also offers valuable theoretical insights and practical guidance for the microstructure design of the insensitive explosives for direct laser ignition.