Inhibition of dissolution-induced crystal transformation of ϵ-Hexanitrohexaazaisowurtzitane in plasticizers by polydopamine coating**

In order to avoid the crystal transformation of ϵ-Hexanitrohexaazaisowurtzitane (ϵ-HNIW) dissolved in plasticizers, a suitable bonding agent was selected to inhibit the crystal transformation of ϵ-HNIW. Interfacial interaction simulations were carried out using Materials Studio2017 software for selected neutral polymer bonding agent (NPBA), polyene polyamine bonding agent (LBA) and polydopamine (PDA) and ϵ-HNIW. Results showed that the interaction order of the three polymers on the ϵ-HNIW crystal surface is PDA>NPBA> LBA; ϵ-HNIW@ PDA crystal phase was more stable. Therefore, ϵ-HNIW@ PDA crystal particles were constructed by the in-situ self-polymerization coating technology. Scanning electron microscope (SEM) showed that the ϵ-HNIW@ PDA was square with smooth surface. The thermal properties of ϵ-HNIW@ PDA were investigated by differential scanning calorimetry (DSC), which showed that the coating of PDA effectively increased the transition temperature of ϵ-HNIW crystal. Moreover, the solubility and crystal transformation mechanism and law of ϵ-HNIW/ϵ-HNIW@ PDA in four plasticizers were further studied and compared systematically, ϵ-HNIW@ PDA showed significantly lower solubility compared with ϵ-HNIW. The solubility size was ranking as isodecyl nonanoate (IDP)>dioctyl sebacate (DOS)>dioctyl adipate (DOA)>paraffin liquid (RH). Variable-temperature X-ray diffraction (XRD) tests showed that PDA increased the ϵ-HNIW crystal transformation temperature by about 35 °C. The small amount of dissolution of ϵ-HNIW by the four plasticizers had a facilitative effect on the ϵ-HNIW crystal transformation, which was consistent with the solubility magnitude. These results indicated that PDA-coated ϵ-HNIW enhances crystal interfacial interaction, reduces the solubility in plasticizers, and has a significant inhibitory effect on the dissolution-induced crystal transformation of ϵ-HNIW.