1. Introduction
Nanothermite has received extensive attention as energetic materials for its excellent thermal, combustion and reaction characteristics with applications in propellants, explosives and pyrotechnics [1-2]. Conventionally, nanothermite consists of two components, a fuel and an oxidizer [1-2]. Comprehensively considering the cost, calorific value and safety, aluminum (Al) nanoparticles is the most popular choice for the fuel[3]. As for oxidizer, there are so many potential candidates, such as copper oxide (CuO), iron oxide (Fe2O3), silicon dioxide (SiO2), manganese dioxide (MnO2), nickel oxide (NiO) [4-10]. Among them, the formula of Al and MnO2 is one of the most promising energetic materials with a high burning rate, an adiabatic temperature and a relatively low ignition point [11]. In nature, fluorine is the most electronegative element in periodic table of elements with the electronegativeity of 3.98 on Pauling scale [12-13]. Thus, recently, the combination of nanothermites and fluorine polymers has aroused wide concern from researchers [14-16].
Fluorine polymers have been already widely used in many applications, such as membrane, tubing, fibers, filler and coating materials, which contain fluorine atoms in the molecular chains [17-19]. The most famous fluorine polymer is polytetrafluroethylene (PTFE) because of the highest fluorine content, about 76% [20]. Tang and his co-author had paid much attention on the mechanical properties and impact-induced characteristics of PTFE/Al/CuO reactive materials [21-22]. The flame and energy release rate greatly improved due to the addition of Al/CuO thermite. Recently, a comparative research reported about three kinds of PTFE-based thermite materials, PTFE/Al/Fe2O3, PTFE/Al/MnO2and PTFE/Al/MoO3 [23]. The results showed that the formula of PTFE/Al/MnO2 released the most energy during compression, and the detailed thermal reaction processes of PTFE/Al/MnO2 was also reported [24]. But the components were mainly at the micron-scale with slow energy release. In fact, because of the poor solubility and agglomeration of PTFE, it is hard to obtain the uniform well-mixed samples, especially for nanothermites, which is also the main drawback for further application in energetic materials field [25]. Thus, poly(vinylidene fluoride-ter-hexafluoropropylene-ter-tetrafluoroethylene) (poly(VDF- ter- HFP-ter - TFE)) terpolymer with both high fluorine content and good solubility can be used as a substitute for PTFE in nanoenergetic materials application [25]. However, few researches focus on the application of poly(VDF- ter- HFP-ter - TFE) on nanothermites.
Therefore, in this paper, poly(VDF- ter- HFP-ter - TFE) terpolymer is selected as energetic additive and binder, and the Al/MnO2/ poly(VDF- ter- HFP-ter - TFE) nanothermite samples are prepared by using electrospray method. The morphologies, thermal properties and combustion performance are investigated. Furthermore, the mechanism of terpolymer on nanothermite system is also discussed and analyzed which will provide a practical guidance for fluorine- containing nanothermite research and application.