Chemical Modification of ß-Cyclodextrins: Balancing Soft and Rigid Domains in Complex Structures.

Crystalline polymers such as ß-cyclodextrin (ßCD) can be modified with polyethylene glycol (PEG) diglycidyl ether cross-linkers (262, 394, 500 Da). In this work, the authors show that the quantity and length of the PEG soft segments influence the solubility and malleability of the products, which are water soluble and easily converted to nitrated analogues under standard reaction conditions. Inert and nitrated derivatives containing longer PEG segments showed the ability to self-heal. The degree of cross-linking and decomposition temperatures and energies depended on the quantity and length of the soft segment. Nitrated cross-linked ßCD containing longer PEG segments did not ignite following an electrostatic discharge of 4.5 J. The chemical stability of ßCD/PEG binders was tested by heat flow calorimetry at 80 °C. The balanced incorporation of soft PEG and rigid ßCD segments was found to improve the processability of cross-linked ßCDs and desensitised their nitrated derivatives, offering new solutions for inert and energetic binders.

Interaction and thermal studies on graphene oxide in NC/DEGDN/GO nanocomposites.

Before considering the uses of graphene oxide (GO) in nitrate ester-based materials for performance and safety improvement, its interaction, compatibility and dispersion with the host matrices need to be well understood. This work addresses the interaction and dispersity of GO with nitrocellulose (NC)/diethylene glycol dinitrate (DEGDN)-based nanocomposites. The GO and DEGDN were successfully synthesised and characterised. The NC/DEGDN proved to be a good hosting matrix for the dispersion of GO nanosheets. Analysis of atomic force microscopy (AFM) showed that the thicknesses of dispersed GO were in the range of 1-4 nm suggesting that the GO in the nanocomposite consists of 1-2 layers for a 0.5% w/w GO containing nanocomposite and 2-4 layers for a 0.75% w/w nanocomposite. ATR-FTIR spectroscopy analysis established red-shifting of 744 to 752 cm-1 for the O-NO2 bond stretching vibrations, indicating bond stabilization by donor electron from the GO. The Raman spectra analysis showed GO peaks blue-shifting and broadening which is attributed to hydrogen bonding interaction between GO sheets and -NO2 groups. The activation energy of nitrate ester decomposition of NC/DEGDN/GO nanocomposites increases as a function of GO content from 167 kJ mol-1 and reaches a maximum of 214 kJ mol-1 for a 0.5% w/w GO loading. This suggests an improvement of the nitrate ester bond stability. These findings open a new direction to the application of GO in nitrate ester-based materials for increased stability, safety and shelf life.

Ultrasonic Studies of Solid Azobenzene-Decorated Polymer Thin Films.

This work investigates the effect of ultrasound on switching of cis azobenzene isomers to their trans counterparts in solid films of methyl methacrylate and methacryloyloxyazobenzene copolymers [P(MMA/MOAB)]. Ultraviolet-visible and 1H nuclear magnetic resonance spectroscopies demonstrate that 46% of the cis isomer converts to the trans form purely by ultrasonic agitation and 46% converts to the trans isomer by localized ultrasound-induced heating effects. Comparative studies of isomerization by ultrasound wave, heat, and visible irradiation show that ultrasound exposure requires a longer time to switch the cis-to-trans conformation. The estimated activation energy for the cis-to-trans conversion in solid polymer films is shown to be comparable to previous values of azobenzene isomerization, indicating that incorporation of the chromophore in a polymeric system affects the kinetics of transition but not the barriers to conformational change.

The spatial distribution patterns of condensed phase post-blast explosive residues formed during detonation.

The continued usage of explosive devices, as well as the ever growing threat of 'dirty' bombs necessitates a comprehensive understanding of particle dispersal during detonation events in order to develop effectual methods for targeting explosive and/or additive remediation efforts. Herein, the distribution of explosive analytes from controlled detonations of aluminised ammonium nitrate and an RDX-based explosive composition were established by systematically sampling sites positioned around each firing. This is the first experimental study to produce evidence that the post-blast residue mass can distribute according to an approximate inverse-square law model, while also demonstrating for the first time that distribution trends can vary depending on individual analytes. Furthermore, by incorporating blast-wave overpressure measurements, high-speed imaging for fireball volume recordings, and monitoring of environmental conditions, it was determined that the principle factor affecting all analyte dispersals was the wind direction, with other factors affecting specific analytes to varying degrees. The dispersal mechanism for explosive residue is primarily the smoke cloud, a finding which in itself has wider impacts on the environment and fundamental detonation theory.

Morphological Variations of Explosive Residue Particles and Implications for Understanding Detonation Mechanisms.

The possibility of recovering undetonated explosive residues following detonation events is well-known; however, the morphology and chemical identity of these condensed phase postblast particles remains undetermined. An understanding of the postblast explosive particle morphology would provide vital information during forensic examinations, allowing rapid initial indication of the explosive material to be microscopically determined prior to any chemical analyses and thereby saving time and resources at the crucial stage of an investigation. In this study, condensed phase particles collected from around the detonations of aluminized ammonium nitrate and RDX-based explosive charges were collected in a novel manner utilizing SEM stubs. By incorporating the use of a focused ion beam during analysis, for the first time it is possible to determine that such particles have characteristic shapes, sizes, and internal structures depending on the explosive and the distance from the detonation at which the particles are recovered. Spheroidal particles (10-210 µm) with microsurface features recovered following inorganic charge detonations were dissimilar to the irregularly shaped particles (5-100 µm) recovered following organic charge firings. Confirmatory analysis to conclude that the particles were indeed explosive included HPLC-MS, Raman spectroscopy, and mega-electron volt-secondary ionization mass spectrometry. These results may impact not only forensic investigations but also the theoretical constructs that govern detonation theory by indicating the potential mechanisms by which these particles survive and how they vary between the different explosive types.