The impact of processing operations such as chemical synthesis conditions, milling, coating and pressing operations on the crystallographic structure of HMX has been studied using X-ray diffraction and Rietveld analysis. Strong differences in grain morphology and X-ray patterns were first observed after synthesis on two different setups with different washing methods. Diffraction pattern refinements were tentatively performed on the basis of known structures and assuming preferential orientations. The impossibility of achieving satisfactory agreement, even considering the orientation of several planes, could be attributed to the presence of polymorphism or hydrates. The possible new polymorphs or hydrates were metastable since milling led to the stable ss-HMX polymorph. No such transformation occurred during the coating operation, but an increase in structural defects was observed. Finally, the pressing step did not induce any transformation but surprisingly led to a decrease in structural defects, probably due to isotropic deformation of the crystallographic cell and the repairing effect of the associated thermal treatment.

Here is described the first synthesis of 5-hydrazino-3-nitro-1,2,4-triazole (HNT), as a free base, from 5-bromo-3-nitro-1,2,4-triazole (BNT) in three steps.

H-1 NMR spin diffusion is shown to advantageously complement scanning electron microscopy (SEM) observations for the characterization of polymer structuring in composite materials. It is here demonstrated on a material containing a few percent of polymer binder and a crystalline organic/inorganic mixture as reinforcement. In SEM observations, polymer accumulations are seen. However, the polymer is also expected to fill small porosities and thin layers at the interface of particles to ensure the cohesion and the mechanical properties of the assembly. In most cases, this polymer structuring is invisible considering the resolution and contrast achieved by SEM on such material. It is thus investigated taking advantage of the two-step decay of nuclear magnetic resonance spin diffusion curves. Average thickness values of 30 and 188 nm are estimated for the interphase and the overall polymer, respectively. Such structural information improves the knowledge of structure/property relationships and provides better understanding of material properties and making processes.

The H2O2vapour cleaves the N–B bond and inhibits the fluorescence of the dixazaborocane.

A number of different quench media were evaluated in order to improve the characteristics of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) obtained via nitration of 2,6-diaminopyrazine-1-oxide (DAPO). After a first screening phase, seven aqueous solutions containing a selected additive were used to quench the nitrating mixture in scale-up experiments. Complete characterization of the resulting LLM-105 indicated that nitrate salts as additives, especially ammonium and potassium nitrate, provided a high quality product, without requiring any further recrystallization. Notably, both particle morphology and thermal stability were significantly improved over the ones obtained using the standard pure water quench. This new DAPO-LLM-105 has been compared to the conventional DMP-LLM-105 and showed similar characteristics with even better insensitivity data.

An original approach has been presented to characterize the local geometry of pores containing protonated small molecule impurities in organic materials. It was here applied in TATB (1,3,5-triamino-2,4,6-trinitrobenzene) powder material to investigate the porosity able to enclose water molecules. The presence of such defects may have a significant impact on TATB-based compositions mechanical properties, efficiency, and shock sensitivity. Apparent self-diffusion coefficients measured on the low water signal residue were consistent with highly mobile species experiencing restricted diffusion in confined porosities. Applying the methodology commonly used for the characterization of porous systems, we could demonstrate for the first time that pores, with an average size in the 3-5 μm range, were already present in the native TATB powder before any formulation and that these pores were closed and filled with water/NH4Cl solutions. The presence of such macrocavities was further confirmed by analyzing the TATB 3D porous structure using the SEM-FIB dual-beam technique at the scale of particle fractions. Calculation of the pore volumes was performed to deduce pore size distributions assuming spherical cavities. A volume-weighted average size was calculated showing a satisfactory agreement with NMR results and a suitable complementarity of the two approaches.

In this article, fluorescent detection method is reported for hydrogen peroxide and more widely for peroxide-based explosives compounds. Using the principle of inhibition of the photo-induced electron transfer (PET), the compound 6(anthracen-9-ylmethyl)-2-phenyl-1,3,6,2-dioxazaborocane has been synthesized and used specifically for the detection of peroxide-based explosives. Upon testing in a laboratory detection prototype under hydrogen peroxide vapors and interfering compounds, this compound appears to be a very promising fluorescent sensor.

During the past decade, the number of terrorism acts has increased and the need for efficient explosive detectors has become an urgent worldwide necessity. A prototype, Nebulex™, was recently developed in our laboratory. Basically, it couples the solubilization of an analyte from the atmosphere by a nebulization process and in-situ detection. This article presents the development and integration of an electrochemical sensor for the detection of nitromethane, a common chemical product that can be used to make an improvised explosive device. A gold screen-printed electrode was used in a flow-cell and a detection limit of 4.5µM was achieved by square wave voltammetry. The detection method was also determined to be selective toward nitromethane over a large panel of interfering compounds. Detection tests with the Nebulex™ were thus carried out using a custom-made calibrated nitromethane vapor generator. Detection times of less than one minute were obtained for nitromethane contents of 8 and 90ppmv. Further measurements were performed in a room-measurement configuration leading to detection times in the range of 1–2min, clearly demonstrating the system׳s efficiency under quasi-real conditions.

During the past ten years, the use of artisanal explosive compositions in terrorism attacks has increased and efficient detectors are greatly needed. Nitromethane is an interesting target for detection due to its uses in artisanal explosive compositions and also for its carcinogenic characteristics. Several techniques including electrochemistry have been developed but require laboratory equipment, preparative steps or complex working electrodes. We here describe the development of a robust, simple and commercially available electrochemical detection system. Square wave voltammetry was used for this purpose with a gold working electrode and a phosphate buffer at pH 7.5. The limits of detection (LOD) were 2.3μM without dissolved oxygen in the solution and 12.5μM in air. Furthermore, a mechanistic investigation enabled us to confirm, under these conditions, a 4-electron reduction mechanism from nitromethane to N-methylhydroxylamine. However, under real conditions of use, N-methylhydroxylamine is not the sole product of the reduction reaction. Other products have been identified by nuclear magnetic resonance characterization and a reaction scheme was established. The system could be minimized for on-site measurements by using screen-printed electrodes with a portable potentiostat. A vapor concentration of 20ppm of nitromethane could be detected within 1min thanks to this electrochemical sensing system.

As of lately, the demand for developing artificial sensors with improved capabilities for the detection of explosives, toxics or drugs has increased. Ideally, sensor devices should provide high sensitivity and give a response that is specific to a given target molecule without being influenced by possible interfering molecules in the atmosphere. These properties strongly depend on the structure of the chemical compound used as a sensitive material. It is thus crucial to select the right compound and this step would be facilitated with the aid of predictive tools. The present investigations have been focused on a family of functionalized polysiloxane polymers deposited on a QCM device, producing only weak interactions compatible with reversible sensors. The quartz frequency variation at equilibrium has been linked to the partition coefficient that was evaluated using a thermodynamic description of the adsorption process. We have shown that the relative responses of two polymers can be directly determined from the Gibbs free enthalpy of mixing as determined from NMR measurements performed on neat liquid mixtures. An equivalence of this term-including both enthalpy and entropy contributions-to the energy interaction term calculated using Hansen solubility coefficients, has been demonstrated previously. These results constitute a basis for the development of a numerical program for calculating equilibrium sensor responses. For small molecules, the adsorption kinetics can be easily accounted for by a Fick diffusion coefficient estimated from the Van der Waals volume.

Molecular mobility and NMR NMR appears as a powerful technique in view of approaching molecular motions. Spin relaxation depends essentially on rotational motions (overall tumbling or internal motions) whereas translational motions are unravelled by self-diffusion coefficients. In this article, the two approaches will be described not only from an experimental point of view (with nowadays elaborated instruments) but also according to their ability at characterizing complex systems. In particular, it will be shown how one can access the size of molecular entities, the various interactions between molecules, the interaction between a spy-molecule and a surface, information about liquid state... Attempts will be made for delineating the application fields of these techniques, as well as their limitations and perspectives.

15N CP/MAS solid state NMR should be a method of choice to obtain essential structural information on organic materials containing nitrogen atoms. However, the technique is generally not selected for the characterization of non‐labelled chemical compounds, which represents the most common situation encountered by chemists. Actually, due to the poor sensitivity of 15N the method is time‐consuming and a very fine calibration is often a prerequisite to reach a sufficient signal/noise. The main drawback comes from the weakness of 15N‐1H dipolar couplings which leads to a splitting of the static Hartman Hahn condition into very narrow sideband conditions under MAS. Practically, it is more difficult to obtain a high enough CP transfer level on 15N for the entire spectrum than on other more conventional nuclei like 13C. An experimental investigation of the CP efficiency using the ramp and adiabatic CP transfer experiments is here proposed. Preliminary adjustments of experimental settings were first made on an 15N‐labeled substituted heterocyclic model system, and then applied to several other organic compounds. Particular attention was paid to the detection of non‐protonated nitrogen atoms with a significant chemical shift anisotropy, which represented the least favourable case. It was experimentally demonstrated that, for these atoms, the adiabatic passage provided a much higher transfer level than the more conventional ramp sequence leading to an enhancement factor of up to 3.5 at a MAS frequency of 30 kHz. The resulting sensitivity rendered possible the detection of non‐protonated nitrogen atoms at natural abundance with 2.5‐mm rotors at 9.4 T. Copyright © 2011 John Wiley & Sons, Ltd.

Organic-inorganic hybrid membranes of poly(vinylidene fluoride)-cohexafluoropropylene (PVdF-HFP) and mesostructured silica containing sulfonic acid groups were synthesized by using the sol-gel process. These hybrid membranes were prepared by in situ co-condensation of tetraethoxysilane and an organically modified silane (ormosil) by a self-assembly route using organic surfactants as templates for tuning the architecture of the hybrid organosilica component. In this paper, we describe the elaboration and characterization of hybrid membranes all the way from the precursor solution to the evaluation of the fuel cell performances. These hybrid materials were extensively characterized by using NMR and IR spectroscopy, electron microscopy, or impedance spectroscopy so as to determinate their physicochemical and electrochemical properties. Even though the ion-exchange capacity (IEC) was quite weak, the first fuel cell tests performed with these hybrid membranes show promising results relative to optimized Nafion 112 thanks to great water management of the silica inside the hydrophobic polymer.

The rational design of new sensitive materials for chemical sensors relies on the knowledge of molecular interactions between the chemical species in question with compounds that may potentially be present in the gas phase. In this context, the intermolecular interactions between a family of functionalized polysiloxanes and a series of organic compounds have been investigated. This work addresses the problem of determining the association constant or energy by studying neat liquid mixtures without solvents. An original approach has been proposed to obtain such information from the excess function of the difference in chemical shifts between both interacting species. Data obtained as a function of the composition of the mixtures have been fitted according to two models: either by considering the formation of a 1:1 complex governed by an equilibrium constant or by the existence of a local composition following the Wilson model. Both methods have been tested on model compounds and the results have been compared with solubility enthalpies calculated using Hansen coefficients.

Interconnected microcellular polymeric monoliths have been prepared from oil-in-water concentrated emulsions of aqueous 1-vinyl-1,2,4-triazole using the high internal phase emulsion methodology. The polyHIPE materials thus obtained present a typical polyHIPE morphology having unexpectedly high mechanical strengths considering their low cross-linking level (3 mol % of N,N′-methylenebis(acrylamide)). 13C, 15N, and 1H solid-state NMR analyses confirm the expected polymer structure and evidenced the presence of polymer chain association by strong hydrogen bonding with water.

A numerical model has been developed to predict the sensitivity of QCM (Quartz Crystal Microbalance) sensors. Such device is coated with a spray-deposited polymer, which has a specific affinity for a given family of molecules: here, nitro aromatic compounds are the target as they are key compounds for explosives trace detection in gas phase. The model is tested by a set of initial measurements performed on several target and interfering molecules. Physico- chemical characterizations are used to validate the model assumptions. The main goal of our approach is twofold: (i) to improve the choice of sensing material for chemical sensor development with a small number of experimental detection tests and (ii) to predict the response of a given material to other analytes.

Mesomeric heteropentalene betaines are conjugated fused polyheterocyclic structures that represent interesting intermediates for organic synthesis. Five such structures, containing at least four nitrogen atoms and various substituents, have been characterized by (1)H, (13)C and (15)N NMR. We report, apparently for the first time, nitrogen NMR data and coupling information on such systems. Inter-ring long-range correlations across five bonds with (15)N ((5)J(HN)) and up to seven bonds with (13)C ((6)J(HC) and (7)J(HC)) were observed in HSQC experiments. The incorporation of an electron-withdrawing substituent such as NO(2) was observed to cause an increase in the magnitude of the remote couplings and deshielding of nearby protons, carbons and on all nitrogen atoms of the structure, including remote ones situated on other cycles.

The stoichiometric noncovalent imprinting of pinacolyl methylphosphonate (PMP), a degradation product of a chemical warfare agent, has been investigated. A rational approach consisting of controlling the number of specific sites produced during the polymerization was carried out in order to design the methacrylic acid (MAA)-based imprinted polymers. The objective of the method was to study by NMR spectroscopy the molecular association process between the monomer (MAA) and the template (PMP) in solution. Accurate variations in the chemical shifts of H-1 and C-13 were determined in a series of samples at various concentrations in the mixture of acetonitrile/toluene (3:1, v/v). By using an elaborated data treatment, we were able to simultaneously determine the stoichiometry, the association constant, and the condensation degree of the resulting complex. On the basis of these results, a stoichiometric noncovalent PMP-imprinted polymer was subsequently synthesized. Adsorption isotherms of the materials were measured and confronted with those of an imprinted polymer conventionally synthesized with excess monomer. These results established for the first time, the feasibility of imprinted polymers with low-molecular-weight and poorly functionalized templates such as pinacolyl methylphosphonate via stoichiometric noncovalent interactions. Batch binding tests were also carried out on a series of three analogue phosphonates in order to elucidate the influence of the functionality, shape, and size of the analyte on the adsorption properties of the polymers.