Multi-scale self-assembly of nanoenergetic materials utilizing functionalized graphene
The work described here-in focuses on the synthesis and characterization of novel nanoenergetic materials and is driven by overcoming the disadvantages of traditional nanoenergetic composites, improving the energetic performance as well as discovering the science boundary of nanoenergetic materials. Micro-scale and macro-scale structured energetic composites were synthesized via self-assembly process between Al nanoparticles, metal oxide nanoparticles and functionalized graphene. A novel gelation process of reduced graphene oxide was developed and utilized for self-assembling Al and Bi2O3 into macroscale structures with enhanced energetic performance and handling safety. The process successfully reduced graphene oxide sheets into rGO, forming a 3D structure with high porosity, controllable density, size, shape and chemical composition. The phase separation between Al and Bi2O3 was minimized, and the energetic reactivity of both nanoparticles was retained. Therefore, the final product rGO/Al/Bi2O3 exhibited 25% increase in energetic release during equilibrium reaction. A more than 100% increase in combustion rate was observed due to the unique self-confining structure. The conductive rGO scaffold offered the product a better safety for handling by increasing the ignition threshold to electrostatic discharge by 4 orders. Halogenated graphene was also adopted as the additive for self-assembly with Al and Bi2O3 nanoparticles for micro-scale energetic composites. A fluorine, oxygen co-functionalized graphene (FGO) was synthesized via a gas -- solid XeF2 -- GO reaction. The stability of this material upon storage time, temperature and dispersing was examined, confirming both stable and unstable fluorine groups contained in its structure. After mixing with Al and Bi2O3 nanoparticles, the FGO/Al/Bi2O3 showed a 60% enhancement in energy release and an all-solid-state reaction between Al and Bi2O3 as the fluorine significantly weakened the alumina shell protecting Al core. Iodinated reduced graphene oxide (I-rGO) was also prepared to fabricate microscale self-assembled I-rGO/Al/Bi2O3. The I-rGO was synthesized by graphene oxide paper and hydroiodic acid, containing both chemically bonded single iodine atoms and intercalated polyiodide clusters between graphene layers. The loss of iodine contents, especially polyiodide clusters, from the structure upon heating, solvent effect and exfoliation was examined. After self-assembly with Al and Bi2O3 nanoparticles, the released iodine weakened the alumina shell by forming Al-O-I bond on it, reducing the reaction temperature and enhancing the energy release significantly. The conductive I-rGO also increased the threshold to electrostatic discharge of final I-rGO/Al/Bi2O3 by 4 orders, ensuring the safety during handling the material in large quantity.
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