Structure and properties of nitrocellulose: approaching 200 years of research.

This review brings together almost 200 years of fragmented research on the structure of nitrocellulose to give an overview that covers production to application in composite materials. As a mouldable plastic, energetic rocket propellant and biomolecular binding membrane, nitrocellulose still finds widespread practical application today despite the inception of synthetic plastics. The influence of different cellulose source materials affects the structure and properties of nitrocellulose in ways that are not fully understood, and so this review brings together relatively recent developments in the understanding of cellulose nanostructures to highlight where the gaps in understanding now reside.

Accounting for super-, plateau- and mesa-rate burning by lead and copper-based ballistic modifiers in double-base propellants: a computational study.

We present a first-principles computational study to understand the action of lead and copper-based ballistic modifiers in the combustion of double-base propellants (DBPs). We show that lead oxide clusters are easily broken down upon addition of small amounts of carbon and the resulting graphitic matrix, dispersed with weakly bound and exposed Pb sites, acts as a Lewis acid to bind small molecule Lewis bases such as NO and CHO that form in the combustion flame. This accounts for super-rate burning, where the fuel burn rate is enhanced.

Is the impact sensitivity of RDX polymorph dependent?

Impact-sensitivity predictions based on the vibrational up-pumping model show a strong polymorph dependency for RDX and highlight that one of the high-pressure forms, which forms during shock-wave experiments, is appreciably more susceptible to mechanical initiation. The origin of the predicted impact sensitivity variation can be attributed to vibrational mode hardening by pressure and to differences in the molecular conformation of RDX in the four polymorphs studied. These polymorphs present different distributions of molecular vibrations within their respective up-pumping windows, which leads to their varying ability to up-pump and trap the vibrational energy that arises from mechanical insult.

Predicting the impact sensitivity of a polymorphic high explosive: the curious case of FOX-7.

The impact sensitivity (IS) of FOX-7 polymorphs is predicted by phonon up-pumping to decrease as layers of FOX-7 molecules flatten. Experimental validation proved anomalous owing to a phase transition during testing, raising questions regarding impact sensitivity measurement and highlighting the need for models to predict IS of polymorphic energetic materials.

Towards Computational Screening for New Energetic Molecules: Calculation of Heat of Formation and Determination of Bond Strengths by Local Mode Analysis.

The reliable determination of gas-phase and solid-state heats of formation are important considerations in energetic materials research. Herein, the ability of PM7 to calculate the gas-phase heats of formation for CNHO-only and inorganic compounds has been critically evaluated, and for the former, comparisons drawn with isodesmic equations and atom equivalence methods. Routes to obtain solid-state heats of formation for a range of single-component molecular solids, salts, and co-crystals were also evaluated.

Triglycerides as Novel Phase-Change Materials: A Review and Assessment of Their Thermal Properties.

Latent Heat Storage (LHS) with Phase-Change Materials (PCMs) represents a high energy density storage technology which could be applied in a variety of applications such as waste heat recovery and integration of renewable energy technologies in energy systems. To increase the sustainability of these storage solutions, PCMs have to be developed with particular regard to bio-origin and biodegradability. Triglycerides represent an interesting class of esters as the main constituents of animal and vegetable fats, with attractive thermal properties.

Towards understanding the catalytic properties of lead-based ballistic modifiers in double base propellants.

Lead-based ballistic modifiers are additives in double base propellants (DBPs) which render the burn rate insensitive to changes in pressure within a defined pressure range, thus imparting greater control of combustion conditions. In-coming European legislation will soon ban the use of lead in propellant formulations, however, and few suitable candidate replacement materials are currently available. In an effort to understand better the unique properties offered by lead-based modifiers, we present a first-principles computational study on Pb, PbO, PbO2, SnO2 and Bi2O3, all of which have been investigated experimentally as ballistic modifier materials.

Synthesis and characterization of the mixed-ligand coordination polymer CuCl(NC-NO).

Reduction of copper(ii) chloride using sodium ascorbate in the presence of pure sodium 5-nitro-tetrazolate (NaNT) forms copper(i) 5-nitrotetrazolate - a known initiatory explosive (DBX-1) - and the novel mixed-ligand copper(i) chloride 5-nitrotetrazolate coordination polymer Cu3Cl(N4C-NO2)2, as well as mixtures of both. The reaction is controlled by the presence of seed crystals and transition metal compounds other than CuCl2. Cu3Cl(N4C-NO2)2 is obtained as a wine-red, air stable, water-insoluble, crystalline and highly sensitive explosive material with a greater crystal density, lower thermal stability and a higher sensitivity toward hydrolysis and shock than DBX-1.

Experimental and simulation study of the high-pressure behavior of squalane and poly-α-olefins.

The equation of state, dynamical properties, and molecular-scale structure of squalane and mixtures of poly-α-olefins at room temperature are studied with a combination of state-of-the-art, high-pressure experiments and molecular-dynamics simulations. Diamond-anvil cell experiments indicate that both materials are non-hydrostatic media at pressures above ∼1 GPa. The equation of state does not exhibit any sign of a first-order phase transition.

A novel crystal form of metacetamol: the first example of a hydrated form.

We report the crystal structure and crystallization conditions of a first hydrated form of metacetamol (a hemihydrate), CHNO·0.5HO. It crystallizes from metacetamol-saturated 1:1 (v/v) water-ethanol solutions in a monoclinic structure (space group P2/n) and contains eight metacetamol and four water molecules per unit cell.

Investigation of the changes in hydrogen bonding accompanying the structural reorganization at 103 K in ammonium iodate.

Neutron powder diffraction has been used to observe the changes in hydrogen bonding that occur as a function of temperature in NDIO and, thus, determine the structural features that occur during the low-temperature (103 K) phase transition. It is shown that in the deuterated material the change is not a phase change per se but rather a structural reorganization in which the hydrogen bonding becomes firmly locked in at the phase transition temperature, and stays in this configuration upon further cooling to 4.2 K.

An acetonitrile-solvated cocrystal of piroxicam and succinic acid with co-existing zwitterionic and non-ionized piroxicam molecules.

This work reports a new acetonitrile (ACN)-solvated cocrystal of piroxicam (PRX) and succinic acid (SA), 2CHNOS·0.5CHO·CHN or PRX:SA:ACN (4:1:2), which adopts the triclinic space group P-1. The outcome of crystallization from ACN solution can be controlled by varying only the PRX:SA ratio, with a higher PRX:SA ratio in solution unexpectedly favouring a lower stoichiometric ratio in the solid product.

Vibrationally induced metallisation of the energetic azide α-NaN.

As initiation of an energetic material requires rupture of a covalent bond, and therefore population of antibonding electronic states, consideration of the electronic band gap has dominated initiation mechanisms for solid state materials. Most prominent are models based on metallisation, where static mechanical perturbation leads to closing of the electronic band gap. This work explores an alternative mechanism for the dynamic metallisation of a model energetic material, where vibrational excitation resulting from mechanical impact is found to induce transient metallisation of α-NaN3.

Ball-free mechanochemistry: in situ real-time monitoring of pharmaceutical co-crystal formation by resonant acoustic mixing.

Resonant acoustic mixing (RAM) is a new technology designed for intensive mixing of powders that offers the capability to process powders with minimal damage to particles. This feature is particularly important for mixing impact-sensitive materials such as explosives and propellants. While the RAM technique has been extensively employed for the mixing of powders and viscous polymers, comparatively little is known about its use for mechanosynthesis.

Labile Low-Valent Tin Azides: Syntheses, Structural Characterization, and Thermal Properties.

The first two examples of the class of tetracoordinate low-valent, mixed-ligand tin azido complexes, Sn(N)(L), are shown to form upon reaction of SnCl with NaN and SnF with MeSiN in either pyridine or 4-picoline (2, L = py; 3, L = pic). These adducts of Sn(N) are shock- and friction-insensitive and stable at r.t.

Carbon dioxide binary crystals the thermal decomposition of RDX at high pressure.

A carbon dioxide and nitrous oxide solid solution has been captured in a diamond anvil cell following the thermal decomposition of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) at high temperatures and pressures. This is the first time a carbon dioxide binary solid has been observed at high pressure. This observation has stimulated low temperature crystallographic studies of this binary system using recently developed gas absorption apparatus and computational modelling.

Challenges of Mechanochemistry: Is In Situ Real-Time Quantitative Phase Analysis Always Reliable? A Case Study of Organic Salt Formation.

Mechanochemical methods offer unprecedented academic and industrial opportunities for solvent-free synthesis of novel materials. The need to study mechanochemical mechanisms is growing, and has led to the development of real-time in situ X-ray powder diffraction techniques (RI-XRPD). However, despite the power of RI-XRPD methods, there remain immense challenges.

Accessing Mefenamic Acid Form II through High-Pressure Recrystallisation.

High-pressure crystallisation has been successfully used as an alternative technique to prepare Form II of a non-steroidal anti-inflammatory drug, mefenamic acid (MA). A single crystal of Form II, denoted as high-pressure Form II, was grown at 0.3 GPa from an ethanolic solution by using a diamond anvil cell.

Temperature dependent solid-state proton migration in dimethylurea-oxalic acid complexes.

The phenomenon of solid-state proton migration within molecular complexes containing short hydrogen bonds is investigated in two dimethylurea-oxalic acid complexes. Extensive characterisation by both X-ray and neutron diffraction shows that proton migration along the hydrogen bond can be induced in these complexes as a function of temperature. This emphasises the subtle features of the hydrogen bond potential well in such short hydrogen bonded complexes, both intrinsically and in the effect of the local crystalline environment.

Pressure-cooking of explosives--the crystal structure of epsilon-RDX as determined by X-ray and neutron diffraction.

The high-pressure, high-temperature epsilon-form of the widely used explosive RDX has been structurally characterised using a combination of diffraction techniques, and a sample of this form has been successfully recovered to ambient pressure.

The digallane molecule, Ga2H6: experimental update giving an improved structure and estimate of the enthalpy change for the reaction Ga2H6(g) --> 2GaH3(g).

Improved methods of analysis and new quantum chemical calculations have been applied to the results of earlier gas-phase electron diffraction (GED) studies of digallane to give what is judged to be the most realistic structure available to date. The principal distances (r(a3,1) in pm) and interbond angles (angle(a3,1) in deg) are as follows (t = terminal, b = bridging): r(Ga..