Examining chemical structure at the interface between a polymer binder and a pharmaceutical crystal with neutron reflectometry

Core-Shell Structured HMX@Polydopamine Energetic Microspheres: Synergistically Enhanced Mechanical, Thermal, and Safety Performances

The solid⁻solid phase transition, poor mechanical properties, and high sensitivity has impeded further practical applications of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) based polymer bonded explosives (PBXs). To address these issues together, a facile and effective route was employed to achieve a coating of polydopamine (PDA) on the surface of explosive crystals via in situ polymerization of dopamine. Additionally, PBXs based on HMX@PDA microcapsules were prepared with a fluoropolymer as polymer binder. Improved storage modulus, static mechanical strength and toughness, and creep resistance has been achieved in as-prepared PDA modified PBXs. The β-δ phase transition temperature of as-obtained PBXs based on conventional HMX (C-HMX)@PDA was improved by 16.3 °C. The friction sensitivity of the C-HMX based PBXs showed a dramatic drop after the PDA coating. A favorable balance proposed in this paper among thermal stability, mechanical properties, and sensitivity was achieved for C-HMX based PBXs with the incorporation of PDA.

Behaviour of crystalline–amorphous interfaces in energetic aggregates subjected to coupled thermomechanical and laser loading

The behaviour of energetic aggregates was investigated for quasi-static compression and high strain rate thermomechanical compression behaviour that is coupled to laser irradiation. A dislocation-density-based crystal plasticity formulation was used to represent energetic crystalline behaviour, a finite viscoelastic formulation was used for the polymer binder and a coupled electromagnetic (EM)–thermomechanical computational scheme was used to predict aggregate response. Aggregates with different crystal sizes were considered to account for physically representative energetic microstructures and to understand the effects of crystal–crystal and crystal–binder interactions. The presence of smaller embedded crystals in the binder ligaments inhibited viscous sliding, and resulted in global hardening of the aggregate, which led to large stress gradients, localized plasticity and dislocation-density accumulation. The embedded crystals also increased scattering of the EM wave within the binder ligaments and increased the localization of EM energy and laser heat generation. Geometrically, necessary dislocation densities and stress gradients were calculated to characterize how hardening at the binder interfaces can lead to strengthening or defect nucleation.

Non-linear viscoelastic properties of TATB-based polymer bonded explosives modified by a neutral polymeric bonding agent

The application of NPBA provides an efficient route to reinforce, toughen, and improve the creep resistance of explosive composites.

Probing interfaces between pharmaceutical crystals and polymers by neutron reflectometry

Pharmaceutical powder engineering often involves forming interfaces between the drug and a suitable polymer. The structure at the interface plays a critical role in the properties and performance of the composite. However, interface structures have not been well understood due to a lack of suitable characterization tool. In this work, we have used ellipsometry and neutron reflectometry to characterize the structure of such interfaces in detail. Ellipsometry provided a quick estimate of the number of layers and their thicknesses, whereas neutron reflectometry provided richer structural information such as density, thickness, roughness, and intermixing of different layers. The combined information allowed us to develop an accurate model about the layered structure and provided information about intermixing of different layer components. Systematic use of these characterization techniques on several model systems suggests that the nature of the polymer had a small effect on the interfacial structure, while the solvent used in polymer coating had a large effect. These results provide useful information on the efforts of engineering particle properties through the control of the interfacial chemistry.