Fabrication of micro/nano spherulitic hierarchical energetic materials via noncrystallographic branching induced by polymer additives: A case study of 2,2′,4,4′,6,6′-hexanitrostilbene (HNS)

In this work, the micro/nano spherulitic hierarchical 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) with the excellent specific surface area was prepared for the first time, which was expected to overcome the agglomeration problems of nanoscale HNS. In detail, poly(N-isopropyl acrylamide) (PNIPAM), polysuccinimide (PSI), and polyvinylpyrrolidone (PVP) were selected as additives to induce forming spherulitic HNS. Leaflike crystals were obtained in the presence of PNIPAM, while spherulitic HNS could be fabricated in the presence of PSI or PVP. And the prepared spherulitic HNS owned nearly 6 times the specific surface area of the raw HNS, with decreased impact sensitivity and advanced melting and decomposition temperatures, demonstrating a good desensitization effect, and a favorable energy release of the hierarchical structure. Moreover, morphological changes under the effect of the molecular weight and concentration of PVP were explored. The approximated morphological evolution of spherulitic HNS was consistent with the classical spherulitic growth by noncrystallographic branching. Furthermore, it was verified that preferential adsorption of PVP and PSI on the HNS inhibits the growth steps of the (200) face and introduces stress to generate crystal defects, which triggers noncrystallographic branching and further spherulitic growth. Overall, the strategy of fabricating micro/nano spherulitic hierarchical energetic materials via polymer-additive induced noncrystallographic branching is promising to solve the problems of nanoscale energetic materials in agglomeration and microscale bulk crystals in low activity.