Nitroglycerin trapping in melamine matrices.

Melamine (Mel) was used as host matrix for liquid nitroglycerin (NG), to prepare Mel/NG solid powdered compounds containing up to 45 wt% of this explosive. The two preparation processes used for this purpose consisted in evaporating a solution of both components, either in ambient conditions or under reduced pressure by the Spray Flash-Evaporation (SFE) process. In Mel/NG materials, amorphous nitroglycerin is distributed in the crystallized melamine matrix as inclusions, which were found to be smaller in size in the material prepared by the SFE process. Mel/NG materials are not stable over time: they gradually lose the nitroglycerin they contain by evaporation.

Formation mechanisms of sub-micron pharmaceutical composite particles derived from far- and near-field Raman microscopy.

Surface enhanced Raman spectroscopy (SERS) and confocal Raman microscopy are applied to investigate the structure and the molecular arrangement of sub-micron furosemide and polyvinylpyrrolidone (furosemide/PVP) particles produced by spray flash evaporation (SFE). Morphology, size and crystallinity of furosemide/PVP particles are analyzed by scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). Far-field Raman spectra and confocal far-field Raman maps of furosemide/PVP particles are interpreted based on the far-field Raman spectra of pure furosemide and PVP precursors. Confocal far-field Raman microscopy shows that furosemide/PVP particles feature an intermixture of furosemide and PVP molecules at the sub-micron scale. SERS and surface-enhanced confocal Raman microscopy (SECoRM) are performed on furosemide, PVP and furosemide/PVP composite particles sputtered with silver (40 nm). SERS and SECoRM maps reveal that furosemide/PVP particle surfaces mainly consist of PVP molecules. The combination of surface and bulk sensitive analyses reveal that furosemide/PVP sub-micron particles are formed by the agglomeration of primary furosemide nano-crystals embedded in a thin PVP matrix. Interestingly, both far-field Raman microscopy and SECoRM provide molecular information on a statistically-relevant amount of sub-micron particles in a single microscopic map; this combination is thus an effective and time-saving tool for investigating organic sub-micron composites.

3D Core-Shell TiO2@MnO2 Nanorod Arrays on Microcantilevers for Enhancing the Detection Sensitivity of Chemical Warfare Agents.

Nanostructured microcantilevers have shown promise for sensing application of molecules in the vapor phase. Nanostructures have improved the molecule capture ability of microcantilevers by highly enhancing the surface of capture. Here, to improve the sensitivity and selectivity of a commercial microcantilever without functionalization, we developed 3D core-shell titanium dioxide@manganese dioxide (TiO2@MnO2) nanorod arrays on a microcantilever, which exhibited a high enhancement in the sensing performance beyond that of 1D nanostructures for the detection of dimethyl methylphosphonate, a simulant of sarin.

Double-side microcantilevers as a key to understand the adsorption mechanisms and kinetics of chemical warfare agents on vertically-aligned TiO2 nanotubes.

Microgravimetric sensor platforms with physico- or chemo-selective interfaces offer promising sensing properties. They are widely used to detect chemical warfare agents (CWAs). However, a comprehensive insight into adsorption mechanisms and interactions between low concentrations of these adsorbates and low-mass adsorbents is still lacking. In this study, we report a complete and detailed analytical method to model the adsorption processes of low traces of vapor-phase DiMethyl MethylPhosphonate (DMMP), a conventional simulant of CWAs, on a double-side nanostructured microcantilever coated with vertically-aligned titanium dioxide nanotubes (TiO2-NTs). We find that the geometrical configuration of NTs plays an important role in the diffusion regimes of molecules during the adsorption. This study shines light on the adsorption and kinetic mechanisms of low-traces DMMP offering opportunities to have a better insight of the adsorption of CWAs on complex nanostructures and to improve microcantilever sensors.

Formation mechanisms of sub-micron pharmaceutical composite particles derived from far-and near-field Raman microscopy / 药物分析学报

Surface enhanced Raman spectroscopy (SERS) and confocal Raman microscopy are applied to investigate the structure and the molecular arrangement of sub-micron furosemide and polyvinylpyrrolidone(furosemide/PVP) particles produced by spray flash evaporation (SFE).Morphology,size and crystallinity of furosemide/PVP particles are analyzed by scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD).Far-field Raman spectra and confocal far-field Raman maps of furosemide/PVP par-ticles are interpreted based on the far-field Raman spectra of pure furosemide and PVP precursors.Confocal far-field Raman microscopy shows that furosemide/PVP particles feature an intermixture of furosemide and PVP molecules at the sub-micron scale.SERS and surface-enhanced confocal Raman microscopy (SECoRM) are performed on furosemide,PVP and furosemide/PVP composite particles sputtered with silver (40 nm).SERS and SECoRM maps reveal that furosemide/PVP particle surfaces mainly consist of PVP molecules.The combination of surface and bulk sensitive analyses reveal that furosemide/PVP sub-micron particles are formed by the agglomeration of primary furosemide nano-crystals embedded in a thin PVP matrix.Interestingly,both far-field Raman microscopy and SECoRM provide molecular information on a statistically-relevant amount of sub-micron particles in a single microscopic map;this combination is thus an effective and time-saving tool for investigating organic sub-micron composites.

Use of Spray Flash Evaporation (SFE) technology to improve dissolution of poorly soluble drugs: Case study on furosemide nanocrystals.

The poor solubility and related low bioavailability are a major concern for a large number of small molecule drugs, both on the market and in development. Several formulation strategies exist to overcome this issue. Among them, particle engineering is of outmost importance. The aim of this work is to present the potential of Spray Flash Evaporation (SFE), a new technology for drug particle engineering. To assess the potential of SFE, we carried out a case study on the nano-crystallization of furosemide, a BCS class IV drug. A thorough characterization of the obtained nanocrystals is presented along with a study of dissolution which highlights the solubility improvement provided by nanocrystals produced via SFE technology. The obtained results show a particle size reduction when compared to the raw material, as well as an increase of the dissolution rate of 4.5-fold.

Double side nanostructuring of microcantilever sensors with TiO2-NTs as a route to enhance their sensitivity.

We reported a new strategy to enhance the sensing performances of a commercial microcantilever with optical readout in dynamic mode for the vapor detection of organophosphorus compounds (OPs). In order to increase significantly the surface area accessible to the molecules in the vapor phase, we nanostructured both sides of the microcantilever with ordered, open and vertically oriented amorphous titanium dioxide nanotubes (TiO2-NTs) in one step by an anodization method. However, due to the aggressive conditions of anodization synthesis it remains a real challenge to nanostructure both sides of the microcantilever. Consequently, we developed and optimized a protocol of synthesis to overcome these harsh conditions which can lead to the total destruction of the silicon microcantilever. Moreover, this protocol was also elaborated in order to maintain a good reflection of the laser beam on one side of the microcantilever towards the position sensitive photodiode and limit the light diffusion by the NTs film. The results related to the detection of dimethyl methylphosphonate (DMMP) showed that TiO2 and the nanostructuring on both sides of the microcantilever with NTs indeed improved the response of the sensor to vapors compared to a microcantilever nanostructured on only one side. The dimensions and morphology of NTs guaranteed the access of molecules to the surface of NTs. This approach showed promising prospects to enhance the sensing performances of microcantilevers.

Surface characterization of nanoscale co-crystals enabled through tip enhanced Raman spectroscopy.

Atomic Force Microscopy coupled with Tip Enhanced Raman Spectroscopy (AFM-TERS) was applied to obtain information about the structure and surface composition of single nano co-crystals. For this purpose, a co-crystalline system consisting of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo-[5.5.0.03,11.05,9]-dodecane (CL-20) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) in a molar ratio of 2 : 1 (CL-20/HMX) was chosen. CL-20/HMX nano-plates were prepared by spray flash evaporation. To ensure co-crystallinity and nanostructures, powder X-ray diffraction and AFM investigations were performed. The results demonstrate that coherence lengths and particle dimensions are on a similar level though coherence lengths appear shorter than measured particle dimensions. According to this fact, defects inside the nano co-crystals are minimized. The co-crystallinity was additionally proven by confocal Raman spectroscopy. Here, marker bands for pristine CL-20 and HMX were chosen which appear in the CL-20/HMX spectrum in an intensity ratio of ∼2.5 : 1 (CL-20 : HMX). Afterwards surface investigations of single CL-20/HMX nano-plates were performed by AFM-TERS. Due to the surface sensitivity of TERS, these experiments reveal that the ratio of the Raman intensities between CL-20 and HMX inverts at CL-20/HMX nano-plate surfaces. Therefore, it is concluded that nano co-crystal surfaces consist of molecular layers of HMX. A theoretical approximation of the normal coordinates of the investigated marker vibrations supports this conclusion since it can exclude the occurrence of the intensity ratio inversion because of the given orientation between CL-20/HMX nano-plates and the Raman scattering system. Based on this finding, an impact ignition mechanism is proposed, enabling explanation of the close impact sensitivity values of ß-HMX and CL-20/HMX.

Detection of Organophosphorous Chemical Agents with CuO-Nanorod-Modified Microcantilevers.

Microcantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper oxide (CuO) nanorods. The synthesis of the nanostructure consists of the oxidation of a copper layer deposited beforehand on the surface of the sample. The oxidation is performed in an alkaline solution containing a mixture of Na(OH) and (NH4)2S2O8. The synthesis procedure was first optimized on a silicon wafer, then transferred to optical cantilever-based sensors. This transfer requires specific synthesis modifications in order to cover all the cantilever with nanorods. A masking procedure was specially developed and the copper layer deposition was also optimized. These nanostructured cantilevers were engineered in order to detect vapors of organophosphorous chemical warfare agents (CWA). The nanostructured microcantilevers were exposed to various concentration of dimethyl methylphosphonate (DMMP) which is a well-known simulant of sarin (GB). The detection measurements showed that copper oxide is able to detect DMMP via hydrogen interactions. The results showed also that the increase of the microcantilever surface with the nanostructures improves the sensors efficiency. The evolution of the detection performances of the CuO nanostructured cantilevers with the DMMP concentration was also evaluated.

Functionalized TiO2 Nanorods on a Microcantilever for the Detection of Organophosphorus Chemical Agents in Air.

We report the fabrication of nanostructured microcantilevers employed as sensors for the detection of organophosphorus (OPs) vapors. These micromechanical sensors are prepared using a two-step procedure first optimized on a silicon wafer. TiO2 one-dimensional nanostructures are synthesized at a silicon surface by a solvothermal method and then grafted with bifunctional molecules having an oxime group known for its strong affinity with organophosphorus compounds. The loading of oxime molecules grafted on the different nanostructured surfaces was quantified by UV spectroscopy. It has been found that a wafer covered by vertically aligned rutile TiO2 nanorods (NRs), with an average length and width of 9.5 µm and 14.7 nm, respectively, provides an oxime function density of 360 nmol cm-2. The optimized TiO2 nanorod synthesis was successfully reproduced on the cantilevers, leading to a homogeneous and reproducible TiO2 NR film with the desired morphology. Thereafter, oxime molecules have been successfully grafted on the nanostructured cantilevers. Detection tests were performed in a dynamic mode by exposing the microcantilevers to dimethyl methylphosphonate (a model compound of toxic OPs agents) and following the shift of the resonant frequency. The nanostructure and the presence of the molecules on a TiO2 NR surface both improve the response of the sensors. A detection limit of 2.25 ppm can be reached with this type of sensor.

Synthesis of zinc oxide nanorods or nanotubes on one side of a microcantilever.

Cantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with zinc oxide (ZnO) nanorods or nanotubes having a diameter of approximately 100 nm and a length of 1 µm. The nanostructure growth was first optimized on a silicon wafer and then transferred to the cantilevers. The ZnO nanorods were grown in an autoclave. The centre of the nanorods was dissolved in order to obtain nanotubes. The dissolution conditions were optimized in order to have the longest etching depth. After 1.25 h in a dissolution solution containing 0.75 wt% of NH3(aq) and 0.75 wt% of cetyltrimethyl ammonium bromide, the longest etching depth was obtained. After the transfer of the syntheses to the cantilevers, nanorods/nanotubes grew on both sides of the cantilever, which prevents the reflection of the laser allowing the resonance frequency measurement. A masking procedure was developed in order to avoid the growth on one face of the cantilever of zinc oxide nanostructures. As far as the authors are concerned, for the first time, zinc oxide nanotubes were synthesized on only one face of cantilevers with optical readout.

Cu(OH)2 and CuO Nanorod Synthesis on Piezoresistive Cantilevers for the Selective Detection of Nitrogen Dioxide.

Self-controlled active oscillating microcantilevers with a piezoresistive readout are very promising sensitive sensors, despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper hydroxide (Cu(OH)2) or with copper oxide (CuO) nanorods. The Cu(OH)2 rods were grown, on a homogeneous copper layer previously evaporated on the top of the cantilever. The CuO nanorods were further obtained by the annealing of the copper hydroxide nanostructures. Then, these copper based nanorods were used to detect several molecules vapors. The results showed no chemical affinity (no formation of a chemical bond) between the CuO cantilevers and the tested molecules. The cantilever with Cu(OH)2 nanorods is selective to nitrogen dioxide (NO2) in presence of humidity. Indeed, among all the tested analytes, copper hydroxide has only an affinity with NO2. Despite the absence of affinity, the cantilevers could even so condensate explosives (1,3,5-trinitro-1,3,5-triazinane (RDX) and pentaerythritol tetranitrate (PETN) on their surface when the cantilever temperature was lower than the explosives source, allowing their detection. We proved that in condensation conditions, the cantilever surface material has no importance and that the nanostructuration is useless because a raw silicon cantilever detects as well as the nanostructured ones.

Aluminum nanopowder: A substance to be handled with care.

Aluminum nanopowders are increasingly used in various areas of research in materials and physical chemistry. Their unconventional properties are still little understood and make their handling sometimes quite hazardous. In this article, we report the case of apparently benign mixtures of Al with sulfuric acid (H2SO4), which violently explode when they are exposed to a flame. The explosions of 100mg samples were observed by high speed video (60000fr/s). These experiments have showed a three-step mechanism, in which the primary hydrogen combustion ignites and disperses the nano-Al/H2SO4 paste in clusters with high velocities (∼100m/s). The combustion of the paste increases the hydrogen release and initiates the explosion of the H2/air mixture, which propagates at high velocities (760-1060m/s). This effect was not observed with micron-sized Al powders, and it is a good illustration of new hazards with nano-Al. Extreme caution is hence recommended to chemists who handle such materials.

Evaluation of the digestibility of solid lipid nanoparticles of glyceryl dibehenate produced by two techniques: Ultrasonication and spray-flash evaporation.

OBJECTIVE: To evaluate the digestibility of Solid Lipid Nanoparticles (SLN) of glyceryl dibehenate prepared either with surfactants by ultrasonication or without surfactant by spray-flash evaporation. METHODS: SLN of glyceryl dibehenate (Compritol® 888 ATO) were produced by two processes: (i) high-shear homogenization with a solution of water-soluble surfactants followed by ultrasonication (ii) and Spray-Flash Evaporation (SFE) of the pure lipid. The digestibility of these nanoparticles was then tested by in vitro lipolysis using a pH-stat apparatus and the assay of glycerides by gel phase chromatography. RESULTS: SLN of glyceryl dibehenate prepared by ultrasonication exhibited a mean particle size of 180nm and showed a limited digestion of the lipid excipient. SLN comprising only glyceryl dibehenate produced by SFE have a mean particle size between 235 and 411nm depending on process parameters. These nanoparticles were not digested by lipases. The presence of surfactant at the lipid/water interface of the SLN seems to be mandatory to allow the adsorption of the lipase and degradation of glyceryl behenate. CONCLUSIONS: Glyceryl dibehenate as a solid particle - even as a SLN - is not digested by pancreatin during in vitro lipolysis test.

The longstanding challenge of the nanocrystallization of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX).

Research efforts for realizing safer and higher performance energetic materials are continuing unabated all over the globe. While the thermites - pyrotechnic compositions of an oxide and a metal - have been finely tailored thanks to progress in other sectors, organic high explosives are still stagnating. The most symptomatic example is the longstanding challenge of the nanocrystallization of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX). Recent advances in crystallization processes and milling technology mark the beginning of a new area which will hopefully lead the pyroelectric industry to finally embrace nanotechnology. This work reviews the previous and current techniques used to crystallize RDX at a submicrometer scale or smaller. Several key points are highlighted then discussed, such as the smallest particle size and its morphology, and the scale-up capacity and the versatility of the process.

High-resolution Raman Spectroscopy for the Nanostructural Characterization of Explosive Nanodiamond Precursors.

The specific attributes of nanodiamonds have attracted increasing interest for electronics or biomedical applications. An efficient synthetic route towards nanodiamonds is via detonation of hexolite (i.e. a mixture of TNT [2,4,6-trinitrotoluene] and RDX [1,3,5-trinitro-1,3,5-triazine]). In particular, detonation of hexolite crystallized by spray flash evaporation (SFE) yields extremely small diamonds (<4 nm). To unravel the detonation mechanism, a structural characterization of the explosives is required but is challenging due to their thermal instability. We demonstrate a combination of conventional Raman spectroscopy and tip-enhanced Raman spectroscopy (TERS) for resolving morphological and structural differences of differently prepared hexolite nanocomposites. The experiments allow for the first time a structural differentiation of individual TNT and RDX crystals and 15-20 nm sized core-shell structures, consequently providing a general approach to investigate the actual composition of mixtures on the nanometer scale.

Surface Functionalization and Electrical Discharge Sensitivity of Passivated Al Nanoparticles.

Passivated aluminum nanoparticles are surface functionalized to elucidate their sensitivity against an electrical discharge. Two size fractions that differ in surface morphology are investigated. Electronic interactions between the partly inert, partly energetic organic molecules used for surface functionalization and the alumina surface are analyzed in detail. The nanoparticle surfaces are modified with the well-established, inert 2-[2-(2-methoxyethoxy)ethoxy]acetic acid, whereas energetic surface modification is achieved using 1,3,5-trinitroperhydro-1,3,5-triazine or the acidic and aromatic 2,4,6-trinitrophenol. A mechanistic model for the chemical surface functionalization of Al nanoparticles is hypothesized and corroborated by comprehensive optical and Fourier transform infrared spectroscopy studies. The surface structures are adjusted by developing a tunable stabilization procedure that prevents sedimentation and hence increases the saturation concentration in the liquid phase and finally affects the sensitivity character in view of electrical discharge ignition of dry powders. Detailed material characterization is conducted using transmission electron microscopy, combined with energy-dispersive X-ray spectroscopy and various absorption spectroscopy techniques (steady state in the infrared and ultraviolet/visible regime). The adjustment of surface structures of the distinct Al nanoparticle samples offers a valuable tool for tuning and tailoring the reactivity, sensitivity, stability, and energetic performances of the nanoparticles, and thereby enables the safe use of these multipurpose nanoparticles.

Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects.

The goal of the protocol described in this article is to prepare aluminothermic compositions (nanothermites) in the form of porous, monolithic objects. Nanothermites are combustible materials made up of inorganic fuel and an oxidizer. In nanothermite foams, aluminum is the fuel and aluminum phosphate and tungsten trioxide are the oxidizing moieties. The highest flame propagation velocities (FPVs) in nanothermites are observed in loose powders and FPVs are strongly decreased by pelletizing nanothermite powders. From a physical standpoint, nanothermite loose powders are metastable systems. Their properties can be altered by unintentional compaction induced by shocks or vibrations or by the segregation of particles over time by settling phenomena, which originates from the density differences of their components. Moving from a powder to an object is the challenge that must be overcome to integrate nanothermites in pyrotechnic systems. Nanothermite objects must have both a high open porosity and good mechanical strength. Nanothermite foams meet both of these criteria, and they are prepared by dispersing a nano-sized aluminothermic mixture (Al/WO3) in orthophosphoric acid. The reaction of aluminum with the acid solution gives the AlPO4 "cement" in which Al and WO3 nanoparticles are embedded. In nanothermite foams, aluminum phosphate plays the dual role of binder and oxidizer. This method can be used with tungsten trioxide, which is not altered by the preparation process. It could probably be extended to some oxides, which are commonly used for the preparation of high performance nanothermites. The WO3-based nanothermite foams described in this article are particularly insensitive to impact and friction, which makes them far safer to handle than loose Al/WO3 powder. The fast combustion of these materials has interesting applications in pyrotechnic igniters. Their use in detonators as primers would require the incorporation of a secondary explosive in their composition.

Nonlinear optical behavior of porphyrin functionalized nanodiamonds: an efficient material for optical power limiting.

The nonlinear optical mechanisms and the optical limiting behavior of porphyrin functionalized detonation nanodiamonds are investigated and compared to the conventional detonation nanodiamonds (DNDs). The optical limiting behavior is characterized by means of nonlinear transmittance, Z-scan, and scattered intensity measurements when submitted to a nanosecond pulsed Nd:YAG laser operating at the second harmonic wavelength. We found that the largest nonlinear attenuation was observed on the 4,4',4'',4'''-(porphyrin-5, 10, 15, 20-tetrayl) tetrakis benzoic acid (PCOOH) suspension. Using Z-scan experiments, it is shown that nonlinear refraction predominates in the unfunctionalized DND suspension, while nonlinear absorption is the most relevant mechanism in the porphyrin functionalized DNDs. Furthermore, a stronger backscattered intensity signal is highlighted for the unfunctionalized DNDs through nonlinear scattering measurements.

Chip calorimetry for the sensitive identification of hexogen and pentrite from their decomposition inside copper oxide nanoparticles.

Smart detection systems for explosive sensors are designed both to detect explosives in the air at trace level and identify the threat for a specific response. Following this need we have succeeded in using microthermal analysis to sensitively identify and discriminate between RDX and PETN explosive vapors at trace level. Once the explosive vapor is trapped in a porous material, heating the material at a fast rate of 3000 K/s up to 350 °C will result in a thermal pattern specifically corresponding to the explosive and its interaction with the porous material. The explosive signatures obtained make it possible to simultaneously identify the presence and the nature of the explosive vapor in just a few milliseconds. Therefore, this also allows the development of multitarget devices using porous material for capturing the vapor combined with microthermal analysis for fast detection and identification. So far it is the first time that chip calorimetry has been used to characterize and identify explosives in vapor state.