"Raincoat for explosives": Surface chemistry approach to control wetting of nitrocellulose with nitroglycerin

Research Progress of Bonding Agents and Their Performance Evaluation Methods

Bonding agents are an important type of additive that are used to increase the interfacial interaction in propellants. A suitable bonding agent can prevent the dewetting between the oxidant and binder, and thus effectively improve the mechanical properties of the propellant. In the current paper, the bonding mechanisms and research progress of different types of bonding agents such as alcohol amine bonding agents, borate ester bonding agents, aziridine bonding agents, hydantoin bonding agents, neutral polymer bonding agents, and so on, are reviewed and discussed. The evaluation methods of their bonding performances including molecular dynamic simulation, contact angle method, in situ loading SEM, characterization analysis, and mechanical analysis are summarized to provide design ideas and reference for future studies.

Improving the surface hydrophobicity by the solvent effect to reduce the water erosion of the CL-20/TNT cocrystal explosive

Explosives should be isolated from the air to reduce the surface erosion by water vapor in the storage and transport processes. The CL-20/TNT cocrystal was chosen as the research object on account of its structural arrangement and weak intermolecular interactions. A relatively extreme assumption that water molecules and the CL-20/TNT cocrystal existed as a solution system on the interface was proposed to investigate the influence mechanism. CL-20/TNT-water interfacial models were constructed, based on four important stable surfaces predicted using crystal morphology theory. The roughness and the electrostatic potential of each surface were analyzed to judge the strength of interactions between the water layer and the cocrystal surface. The effects of the water layer on the crystal surfaces were quantified in terms of binding energy and the radial distribution function using molecular dynamics simulations. Based on the analysis above, the (0 0 2) face was identified as the least affected by water erosion and its growth should be promoted. The crystal morphologies obtained by crystallization in different solvents are significantly different on account of the solvent effect, which can be used to search for a suitable solvent for crystallization to obtain a cocrystal with a larger hydrophobic surface.

Tuning morphology of Pickering emulsions stabilised by biodegradable PLGA nanoparticles: How PLGA characteristics influence emulsion properties

In this study, we proved that the stabilisation of Pickering emulsions by polymer nanoparticles (NPs) heavily depends on polymer characteristics. We prepared NPs with four poly(lactide-co-glycolide) polymers (PLGA), of different molar masses (14,000 and 32,000 g/mol) and end groups (acid or alkylester). NPs were either bare (without stabilising polymer) or covered by polyvinyl alcohol (PVA). Pickering emulsions were prepared by mixing NP aqueous suspensions with various amounts of oil (Miglyol 812 N). First, NP wettability was directly affected by PLGA end group: ester-ending PLGA led to more hydrophobic NPs, compared to acid-ending PLGA. This effect of the end group could be slightly enhanced with smaller molar mass. Thus, bare PLGA NPs stabilised different types of emulsions (W/O/W and W/O), following Finkle's rule. However, the effect of PLGA characteristics was masked when NPs were covered by PVA, as PVA drove the stabilisation of O/W emulsions. Secondly, PLGA molar mass and end group also influenced its glass transition temperature (T_g), with spectacular consequences on emulsion formation. Indeed, the shortest ester-ending PLGA exhibited a T_g close to room temperature, when measured in the emulsion. This T_g, easily exceeded during emulsification process, led to a soft solid emulsion, stabilised by a network of NP debris.

High-substitute nitrochitosan used as energetic materials: Preparation and detonation properties

In order to develop new high-energy materials utilizing natural products, a high-substitute nitrochitosan was prepared with different methods. Prepared processes and detonation properties of the nitrochitosan samples were systematically studied. The nitration substitute degree, nitrogen content, exothermic decomposition enthalpy, heat of combustion, impact sensitivity, detonation velocity and detonation pressure of the prepared high-substitute nitrochitosan were 2.01, 16.67 %, -2226 J g^-1, -7831.6 ± 116.3 J g^-1, >14.2 J, 7.81 km s^-1, and 24.03 GPa, respectively. Compared with nitrocellulose (NC), the nitrogen content, impact sensitivity and detonation properties of the prepared nitrochitosan were significantly improved. Nitrochitosan and RDX can form a uniform composite in acetone. With the increase of RDX content, the impact sensitivity of composite increased, but the composite was more stable and not easy to decompose. High-substitute nitrochitosan presents a potential application in solid propellants.