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Multi-principal element nanoparticles are an emerging class of materials with potential applications in medicine and biology. However, it is not known how such nanoparticles interact with bacteria at nanoscale. In the present work, we evaluated the interaction of multi-principal elemental alloy (FeNiCu) nanoparticles with Escherichia coli ( E. coli ) bacteria using the in situ graphene liquid cell (GLC) scanning transmission electron microscopy (STEM) approach. The imaging revealed the details of bacteria wall damage in the vicinity of nanoparticles. The chemical mappings of S, P, O, N, C, and Cl elements confirmed the cytoplasmic leakage of the bacteria. Our results show that there is selective release of metal ions from the nanoparticles. The release of copper ions was much higher than that for nickel while the iron release was the lowest. In addition, the binding affinity of bacterial cell membrane protein functional groups with Cu, Ni, and Fe cations is found to be the driving force behind the selective metal cations' release from the multi-principal element nanoparticles. The protein functional groups driven dissolution of multielement nanoparticles was evaluated using the density functional theory (DFT) computational method, which confirmed that the energy required to remove Cu atoms from the nanoparticle surface was the least in comparison with those for Ni and Fe atoms. The DFT results support the experimental data, indicating that the energy to dissolve metal atoms exposed to oxidation and/or the to presence of oxygen atoms at the surface of the nanoparticle catalyzes metal removal from the multielement nanoparticle. The study shows the potential of compositional design of multi-principal element nanoparticles for the controlled release of metal ions to develop antibacterial strategies. In addition, GLC-STEM is a promising approach for understanding the nanoscale interaction of metallic nanoparticles with biological structures.

Dithiothreitol (DTT)-based displacement is widely utilized for separating ligands from their gold nanoparticle (AuNP) conjugates, a critical step for differentiating and quantifying surface-bound functional ligands and therefore the effective surface density of these species on nanoparticle-based therapeutics and other functional constructs. The underlying assumption is that DTT is smaller and much more reactive toward gold compared with most ligands of interest, and as a result will reactively displace the ligands from surface sites thereby enabling their quantification. In this study, we use complementary dimensional and spectroscopic methods to characterize the efficiency of DTT displacement. Thiolated methoxypolyethylene glycol (SH-PEG) and bovine serum albumin (BSA) were chosen as representative ligands. Results clearly show that (1) DTT does not completely displace bound SH-PEG or BSA from AuNPs, and (2) the displacement efficiency is dependent on the binding affinity between the ligands and the AuNP surface. Additionally, the displacement efficiency for conjugated SH-PEG is moderately dependent on the molecular mass (yielding efficiencies ranging from 60 to 80% measured by ATR-FTIR and ≈90% by ES-DMA), indicating that the displacement efficiency for SH-PEG is predominantly determined by the S-Au bond. BSA is particularly difficult to displace with DTT (i.e., the displacement efficiency is nearly zero) when it is in the so-called normal form. The displacement efficiency for BSA improves to 80% when it undergoes a conformational change to the expanded form through a process of pH change or treatment with a surfactant. An analysis of the three-component system (SH-PEG + BSA + AuNP) indicates that the presence of SH-PEG decreases the displacement efficiency for BSA, whereas the displacement efficiency for SH-PEG is less impacted by the presence of BSA.

Electrospray-differential mobility analysis (ES-DMA) is a versatile technique used to aerosolize bionanoparticles and measure their electrical mobility at ambient conditions. ES-DMA is similar to electrospray-mass spectrometry (ES-MS), but measures the effective particle size, rather than mass. It has a wide range of applications and nominally can be used to characterize biomolecules and nanoparticles ranging in size from a few nanometers (~3 nm) to several hundred nanometers, to obtain multimodal size distributions in minutes. Although both the ES and the DMA are mature technologies, they are finding increased use in combination to characterize particles in liquids. In this paper, we review ES-DMA, and how it has recently been used to characterize bionanoparticles such as polymers, proteins, viruses, bacteriophages and nanoparticle-biomolecule conjugates., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Here we demonstrate a rapid and quantitative means to characterize the size and packing structure of small clusters of nanoparticles in colloidal suspension. Clustering and aggregation play important roles in a wide variety of phenomena of both scientific and technical importance, yet characterizing the packing of nanoparticles within small clusters and predicting their aerodynamic size remains challenging because available techniques can lack adequate resolution and sensitivity for clusters smaller than 100 nm (optical techniques), perturb the packing arrangement (electron microscopies), or provide only an ensemble average (light scattering techniques). In this article, we use electrospray-differential mobility analysis (ES-DMA), a technique that exerts electrical and drag forces on the clusters, to determine the size and packing of small clusters. We provide an analytical model to determine the mobility size of various packing geometries based on the projected area of the clusters. Data for clusters aggregated from nominally 10 nm gold particles and nonenveloped viruses of various sizes show good agreement between measured and predicted cluster sizes for close-packed spheres.

The kinetics of the reaction between soot nanoparticles and molecular oxygen were studied by tandem differential mobility analysis (TDMA). The particles were extracted from the tip of an ethene diffusion flame. Reactions were studied at atmospheric pressure in mixtures of nitrogen and oxygen. The studies involved particles of an initial mobility diameter of 30 nm over broad ranges of temperature (500-1100 degrees C) and oxygen volume fraction (0-1). Measurements as a function of oxygen partial pressure establish that the oxidation kinetics are not first-order in oxygen volume fraction (F(O2)). Rather, the oxidation rate increases rapidly and linearly with F(O2) between 0 and 0.05 and then more slowly but still linearly between 0.05 and 1. Temperature dependent measurements are consistent with a reaction pathway involving two kinetically distinguishable oxidation sites which interconvert thermally and through oxidation. Results and conclusions are compared to those of earlier studies on the oxidation of soot.

Reduced diffusion length scales and increased specific surface areas of nanosized metal fuels have recently demonstrated increased reaction rates for these systems, increasing their relevance in a wide variety of applications. The most commonly employed metal fuel, aluminum, tends to oxidize rapidly near its melting point (660 °C) in addition to undergoing a phase change of the nascent oxide shell. To further expand on the understanding of nanosized metal fuel oxidation, tantalum nanoparticles were studied due to their high melting point (3017 °C) in comparison to aluminum. Both traditional slow heating rate and in-situ high heating rate techniques were used to probe the oxidation of tantalum nanoparticles in oxygen containing environments in addition to nanothermite mixtures. When oxidized by gas phase oxygen, the oxide shell of the tantalum nanoparticles rapidly crystallized creating cracks that may attribute to enhanced oxygen diffusion into the particle. In the case of tantalum based nanothermites, oxide shell crystallization was shown to induce reactive sintering with the metal oxide resulting in a narrow range of ignition temperatures independent of the metal oxide used. The oxidation mechanism was modeled using the Deal-Grove model to extract rate parameters, and theoretical burn times for tantalum based nanocomposites were calculated. [ABSTRACT FROM AUTHOR]

The word "nanoparticle" nominally elicits a vision of an isolated sphere; however, the vast bulk of nanoparticulate material exists in an aggregated state. This can have significant implications for applications such as combustion, catalysis, and optical excitation, where particles are exposed to high temperature and rapid heating conditions. In such environments, particles become susceptible to morphological changes which can reduce surface area, often to the detriment of functionality. Here, we report on thermally-induced coalescence which can occur in aluminum nanoparticle aggregates subjected to rapid heating (106-1011 K/s). Using dynamic transmission electron microscopy, we observed morphological changes in nanoparticle aggregates occurring in as little as a few nanoseconds after the onset of heating. The time-resolved probes reveal that the morphological changes initiate within 15 ns and are completed in less than 50 ns. The morphological changes were found to have a threshold temperature of about 1300 ± 50 K, as determined by millisecond-scale experiments with a calibrated heating stage. The temperature distribution of aggregates during laser heating was modeled with various simulation approaches. The results indicate that, under rapid heating conditions, coalescence occurs at an intermediate temperature between the melting points of aluminum and the aluminum oxide shell, and proceeds rapidly once this threshold temperature is reached. [ABSTRACT FROM AUTHOR]

Efficient electrocatalysts are critical in various clean energy conversion and storage systems. Polyelemental nanomaterials are attractive as multifunctional catalysts due to their wide compositions and synergistic properties. However, controlled synthesis of polyelemental nanomaterials is difficult due to their complex composition. Herein, a one‐step synthetic strategy is presented to fabricate a hierarchical polyelemental nanomaterial, which contains ultrasmall precious metal nanoparticles (IrPt, ≈5 nm) anchored on spinel‐structure transition metal oxide nanoparticles. The polyelemental nanoparticles serve as excellent bifunctional catalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The mass catalytic activity of the polyelemental nanoparticles is 7‐times higher than that of Pt in ORR and 28‐times that of Ir in OER at the same overpotentials, demonstrating the high activity of the bifunctional electrocatalyst. This outstanding performance is attributed to the controlled multiple elemental composition, mixed chemical states, and large electroactive surface area. The hierarchical nanostructure and polyelemental design of these nanoparticles offer a general and powerful alternative material for catalysis, solar cells, and more. [ABSTRACT FROM AUTHOR]

The authors present insights on their study wherein they directly observed timescales of morphological change for aluminum nanoparticles and aluminum copper oxide (Al-CuO) nanocomposite thermite using dynamic transmission electron microscopy. Topics discussed include the use of coalescing and sintering into much larger particles, the thin spots in the oxide shell between two metal cores, and the ejection of some particles from the agglomerate during the occurrence of dispersion.

This study explores the reaction between Al and Bi2O3nanoparticles under high heating rate conditions with temperature-jump/time of flight mass spectrometry (T-Jump/TOFMS), high speed imaging, and rapid sample heating within a scanning electron microscope (SEM). Comparison of rapid heating of Al/Bi2O3thermite and neat Bi2O3shows that initiation of the Al/Bi2O3reaction occurs at a much lower temperature than the point where oxygen is released from the neat Bi2O3powder. Thus, without the presence of a gas phase oxidizer, it can be concluded that a condensed phase initiation mechanism must be at play in the Al/Bi2O3nanothermite. C/Bi2O3heating experiments were used for a mechanistic comparison between two different fuel types since the carbon represents a nonvolatile fuel in contrast to the aluminum. This formulation showed a similar condensed phase initiation as was seen with the aluminum nanothermite. Qualitative comparison of high speed imaging for Al/Bi2O3and Al/CuO indicates that the initiation reaction in Al/Bi2O3is about twice as fast as a comparable copper oxide system, which has not been apparent from bulk thermite combustion studies. Bi2O3is known to possess unique ion transport properties, which combined with the presence of oxygen and aluminum ions within the nanothermite system may play a significant role in the speed of the nanothermite reaction. [ABSTRACT FROM AUTHOR]

Abstract: It is axiomatic that the burning time dependence on particle size follows an integer power law dependence. However, a considerable body of experimental data show a power dependence less than unity. In this paper, we focus on what might be responsible for the fractional power dependence observed for the burning time for nanoparticles (e.g. Al and B). Specifically we employ reactive molecular dynamics simulations of oxide-coated aluminum nanoparticles (Al-NPs). Since most nanomaterials experimentally investigated are aggregates, we study the behavior of the simplest aggregate – a doublet of two spheres. The thermo-mechanical response of an oxide coated Al-NP is found to be very different than its solid alumina counterpart, and in particular we find that the penetration of the core aluminum cations into the shell significantly softens it, resulting in sintering well below the melting point of pure alumina. For such coated nanoparticles, we find a strong induced electric field exists at the core–shell interface. With heating, as the core melts, this electric field drives the core Al cations into the shell. The shell, now a sub-oxide of aluminum, melts at a temperature that is lower than the melting point of aluminum oxide. Following melting, the forces of surface tension drive two adjacent particles to fuse. The characteristic sintering time (heating time + fusion time) is seen to be comparable to the characteristic reaction time, and thus it is quite possible for nanoparticle aggregates to sinter into structures with larger length scales, before the bulk of the combustion can take place. This calls into question what the appropriate ‘effective size’ of nanoparticle aggregates is. [Copyright &y& Elsevier]

There is currently a need for low oxide content nanoaluminum as a component in high-energy-density fuels. A gas-phase passivation coating of perfluoropentanoic acid on in situ generated bare nanoaluminum accomplished in an aerosol stream and resulting in an air-stable product is demonstrated. Transmission electron microscopy inspection demonstrates a 1-2 nm coating layer, and thermogravimetric analysis reveals an 80% active fuel content, an increase of 17% from untreated product. X-ray photoelectron spectroscopy confirms both the presence of the fluorocarboxylic acid on the aluminum surface and the thinner coating layer compared with the untreated case. A bridge bonding coordination between the carboxylate group and aluminum is indicated via Fourier transform infrared spectroscopy. The coated product demonstrates reduced ignition temperature in thermite combinations for temperature-jump fine wire combustion tests and X-ray photoelectron spectroscopy verifies formation of AlF3 in burned product. [ABSTRACT FROM AUTHOR]

The article presents an illustration of nanoenergetic gas generators based on periodate salts. It notes the development of versatile aerosol spray drying approach to make periodate salt nanoparticles using the scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, it provides information on the relative reactivity of nanoenergetic formulations of periodate.

The objective of this work is to understand the charging dynamics of metal nanoparticles under wavelength-selected UV irradiation, with a particular focus on the effect of particle structure on the quantum yield. We employed an ion mobility analysis technique to measure the size-resolved single charging efficiency of structure-controlled silver nanoparticles (spheres vs. aggregates) in the mobility diameter (Dm) range of 10 ∼ 100 nm. We found that the measured particle charging efficiency followsD2mdependence for both spherical and aggregate particles. Based on the measured charging efficiency and calculated particle photon absorption cross section, we are also able to determine the mobility size dependence of photoelectric quantum yield for both spheres and aggregates. The quantum yield of spheres is a constant for larger particles (50 nm or larger) but significantly enhanced as particle size decreases. The quantum yield of aggregates is shown to be particle structure dependent and does not behave as a simple summation of individual primary particles. The aggregate particles have higher quantum yield compared with spheres of the same mobility size but is offset by the lower photon absorption cross section, and thus overall charging efficiency of aggregates is lower than spheres of the same mobility size. Copyright 2013 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Abstract: In this Letter, we employed an ion mobility technique to measure the size-resolved native work function of structure controlled nanoparticles in free flight. We found that the Fowler–Nordheim law is applicable to not only spheres but also aggregates. The measured work functions of spheres are size dependent, and consistent with classical image and Coulomb potentials explanations. On the other hand, the measured work functions of aggregates are independent of mobility size, but depend on the size of primary particles. In addition, the particle photoelectric yield of aggregates and spheres were also evaluated as function of incident photon energy. [Copyright &y& Elsevier]

A combination of a differential mobility analyzer (DMA) and aerosol particle mass analyzer (APM) is used to measure the mass of NIST Standard Reference Materials (SRM®) PSL spheres with 60 and 100 nm nominal diameter, and NIST traceable 300 nm PSL spheres. The calibration PSL spheres were previously characterized by modal diameter and spread in particle size. We used the DMA to separate the particles with modal diameter in a narrow mobility diameter range. The mass of the separated particles is measured using the APM. The measured mass is converted to diameter using a specific density of 1.05. We found that there was good agreement between our measurements and calibration modal diameter. The measured average modal diameters are 59.23 and 101.2 nm for nominal diameters of 60 and 100 nm (calibration modal diameter: 60.39 and 100.7 nm) PSL spheres, respectively. The repeatability uncertainty of these measurements is reported. For 300 nm, the measured diameter was 305.5 nm, which is an agreement with calibration diameter within 1.8%. The effect of spread in particle size on the APM transfer function is investigated. Two sources of the spread in “mono-dispersed” particle size distributions are discussed: (a) spread due to the triangular DMA transfer function, and (b) spread in the calibration particle size. The APM response function is calculated numerically with parabolic flow through the APM and diffusion broadening. As expected from theory, the calculated APM response function and measured data followed a similar trend with respect to APM voltage. However, the theoretical APM transfer function is narrower than the measured APM response. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate gas-phase (aerosol) generation of diameter-controlled carbon nanotubes (CNTs) by employing size-controlled monodisperse nickel nanoparticles produced by the combination of pulsed laser ablation and electrostatic classification. The electrostatic classifier sorted agglomerated mono-area nickel particles, and then a subsequent heating process at ∼1200 °C created sintered single primary particles with very narrow size distribution. These isolated single primary particles were then sent to an aerosol reactor where free-flight CNTs were grown with acetylene and hydrogen mix at temperature of ∼750 °C. The resulting CNTs formed in this continuous gas-phase process were found to have a uniform diameter, which is commensurate with the diameter of the size-controlled catalytic nickel particles. [Copyright &y& Elsevier]

Nanomaterials comprising earth-abundant elements show great potential as substitutes for scarce, expensive materials in energy conversions, but degradation and contamination issues in working environments severely limit their practical applications. Here we report a facile and scalable strategy to synthesize ultrathin-graphene-coated cobalt nanoparticles which are achieved by the application of an electrical current pulse to a carbon-based substrate and by generating a transient high temperature of up to 1500 K in 50 ms to induce the nanoparticle growth and graphene coating. Thickness of the graphene shell is effectively controlled to be under three atomic layers, favorable for charge transfer and electrocatalytic applications. Our one-step synthetic strategy provides a universal, scalable and cost-effective approach for the fast synthesis of metal-carbon core-shell nanoarchitectures for energy conversion applications. ga1 • A scalable strategy to synthesize ultrathin-graphene-coated metal nanoparticles. • Thickness of the graphene shell is controlled under three atomic layers. • This approach presents its universality, applicable to various substrates and transition metal elements. • A structure favorable for charge transfer and electrocatalytic applications. [ABSTRACT FROM AUTHOR]

To observe the agglomeration, an important parasitic process in metal composite combustion, sandwiched structures with laminates of aluminum (Al) and ammonia perchlorate (AP) layers are prepared and characterized by high-speed macro and microscopic imaging systems with pyrometry. The bilayer structure prepared by electrospraying was confirmed by Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) and the composition was confirmed by thermogravimetric analysis/differential thermal calorimetry (TGA/DSC). We found that the burn rate of the Al/AP sandwich films increases with the decrease of bilayer thickness of Al and AP, owing to the shorter diffusion distance between fuel and oxidizer. More importantly, the complete process of the agglomeration/sintering of Al nanoparticles (NPs) is observed in-situ, which demonstrates the different stages of agglomeration process of Al NPs. Temperature measurement from pyrometry reveals the temperature of agglomerates during combustion, consistent with the agglomerate size and burn rate observation. Simple calculations based on "pocket-theory" support the observed changes in agglomeration size with bilayer thickness. [ABSTRACT FROM AUTHOR]

Addition of metal and metal oxide nanoparticles to hydrocarbon fuels has shown the ability to increase the volumetric energy density, decrease ignition delay, increase heat of combustion, and catalyze fuel decomposition in recent research. However, energetic metal nanoparticles are prone to aggregation, which occurs at an increased rate near the regressing surface of a burning liquid droplet where local concentrations increase and can form a transport-inhibiting shell, ultimately decreasing the droplet burning rate. Alternatively, gas ejections from the droplet can disrupt shell formation and transport nanoparticles from the droplet to the flame zone. This study quantifies up to a 12.1% decrease in the burning rate constant of Kerosene droplets when 6.1 wt% nanoaluminum (nAl) particles are added (the maximum stable loading) with a hydrocarbon-based surfactant in a free-falling single droplet combustion experiment. Addition of nitrocellulose (NC) particles to the nanofuel diminishes or fully counteracts the burning rate decreases and provides a means of tuning the burning rate constant higher than that of pure Kerosene (maximum 13.8% increase over control with 2.3 wt% nAl and 0.6 wt% NC added). To reach stable nanofuels at higher particle loadings up to 15.0 wt% solid additives, nAl and NC were electrosprayed into composite mesoparticles (MP) before suspending with surfactant in Kerosene. These MP-based nanofuels boast increased dispersibility and additive loadings and thus higher achievable burning rates (maximum 26.5% increase over control) than physically mixed analogs. A mechanism is proposed in which droplet disruptions influenced by NC addition include cyclical inflations, during which the liquid gasification rate increases, e.g. by expanding the outer surface area of the droplet. [ABSTRACT FROM AUTHOR]

Abstract: We show a low temperature gas-phase synthesis route to produce faceted aluminum crystals in the aerosol phase. Use of triisobutylaluminum whose decomposition temperature is below the melting point of elemental aluminum enabled us to grow nanocrystals from its vapor. TEM shows both polyhedral crystalline and spherical particle morphologies, but with the addition of an annealing furnace one can significantly enhance the production of just the polyhedral particles. The results on surface passivation with oxygen suggest that these nanocrystals are less pyrophoric than the corresponding spherical aluminum nanoparticles, and combustion tests show an increase in energy release compared to commercial nanoaluminum. [ABSTRACT FROM AUTHOR]

Abstract: An experimental investigation of the combustion characteristics of boron nanoparticles in the post flame region of a flat flame burner has been conducted. Boron is attractive as a fuel or a fuel supplement in propellants and explosives due to its high heats of combustion on both a gravimetric and volumetric basis. A relatively large database exists for combustion characteristics of large (greater than 1 μm) boron particles, but very little exists for nano-sized boron. Ignition and combustion characteristics have been studied in the post flame region of a fuel lean CH4/Air/O2 flame, with burner temperatures ranging from about 1600 K to 1900 K, and oxygen mole fractions ranging between 0.1 and 0.3. As in earlier investigations on boron combustion, a two-stage combustion phenomenon was observed. Ensemble-averaged burning times of boron nanoparticles were obtained, while the ignition time measurements for boron nanoparticles were extended into a lower temperature range previously unavailable in the literature. The measured burning times were between 1.5 ms and 3.0 ms depending on both the temperature and oxygen mole fraction. The ignition times were relatively insensitive to oxygen concentration in the range studied, and were affected only by temperature. The measured ignition times were inversely related to the temperature, ranging from 1.5 ms at 1810 K to 6.0 ms at 1580 K. The burning time results were compared to both diffusion and kinetic limited theories of particle combustion. It was found that the size dependence on particle burning times did not follow either theory. [Copyright &y& Elsevier]

Aerosol spray coupled with high-temperature pyrolysis is an emerging technique for continuous manufacturing of nanomaterials at large scale that demonstrates extremely high production efficiency. Current aerosol spray techniques using a tube furnace can only attain a low temperature range (generally <1500 K), rendering limited products as well as inhomogeneous heating within the comparatively bulky furnace chamber (typical dimensions of ≥2 cm in diameter and ≥40 cm in length), which leads to difficulties in product quality control. Here we report a "droplet-to-particle" aerosol technique coupled with a high-temperature (∼2000 K) micro-channel reactor, which provides ∼100-times smaller dimensions compared to conventional tube furnaces, enabling homogeneous and high-temperature nanomaterial manufacturing. To demonstrate the unique capability of this carbonized wood micro-channel reactor, we successfully synthesized multielement high entropy alloy/oxide nanoparticles (which typically require a high temperature (2000 K) to achieve uniform elemental mixing) in a continuous and support-free manner. Droplets atomized from the multielement precursors fly through the micro-channels heated to 2000 K by Joule heating with a residence time of only tens of milliseconds with a high energy conversion efficiency (>95%), during which salt decomposition and particle nucleation/growth occur. The high temperature critically enables homogeneous mixing of elements in the resultant nanoparticles and the short residence time is key to suppress particle growth and agglomeration. Compared with the traditional aerosol spray pyrolysis, the carbonized wood reactor can achieve a record high temperature (≥2000 K), a much shorter residence time (∼tens of milliseconds), highly efficient, uniform heating, and provide a platform for continuous nanomaterial manufacturing for a broad range of applications. [ABSTRACT FROM AUTHOR]

Metallized energetic composite films incorporating high mass loadings of aluminum nanoparticle fuels and metal oxide oxidizers (thermite) within a polyvinylidene fluoride (PVDF) polymer matrix were constructed via repeatable direct write additive manufacturing (3-D Printing). High speed videography, Temperature-Jump/Time of Flight Mass Spectrometry (T-Jump/TOFMS), and 2D spaciotemporal temperature mapping were used to analyze the role of composition and particle loading with respect to ignition behavior and combustion performance. This study reveals that, while the ignition temperatures of films are relatively unvaried in pressurized environments, ignition temperatures in vacuum are strongly dependent on the inclusion of thermite material and the specific type of thermite utilized. Increasing thermite mass loading results in a reduction in film flame speed and mechanical integrity but increases flame temperature. Coupled time of flight mass spectrometry reinforces and elaborates on previous findings regarding the Al/PVDF reaction mechanism as it pertains to the coupled behavior of incorporating increasing amounts of metal oxides. TOFMS highlights carbon dioxide generation from the metal oxide interaction with PVDF, leading to unintended stoichiometric considerations and distinct changes in steady burn behavior which contribute adverse factors towards flame propagation. [ABSTRACT FROM AUTHOR]

Metallizing and gelling hydrocarbons has received attention since the 1960s, but slurry fuels utilizing micron particles suffer from long particle burning times and problematic agglomeration. This study investigates single droplet combustion of kerosene with oxygen-containing nanoparticle additives, assembled by electrospray into nitrocellulose (NC)-bound composite “mesoparticle” (MP) structures (on the order of 5 µm). We find significantly improved dispersion properties of these materials compared to unassembled nanoparticles. Droplet combustion is characterized with a free-falling droplet experiment utilizing high speed videography. The MP pre-assembly strategy demonstrated previously by this group to improve burning rate effects and suspension stability of nanoaluminum is extended to oxygen-containing nanoparticles of CuO, KIO 4 , MgO, and Al 2 O 3 added to kerosene as NC-bound MPs. Burning rate enhancements of up to 40% are seen for CuO and KIO 4 MPs. Direct observation of droplet combustion disruptions is used to propose active mechanisms for each additive. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-yield, large scale additive manufacturing of energetic materials. • Nanoparticles assembled into micron size particles with a polymer binder. • Alleviation of reactive sintering by adding low temperature decomposing polymer. • Achieving large scale production without compromising particle size and morphology. • Achieving ∼2–7 fold higher reactivity than physically mixed counterparts. Electrospray has been demonstrated to assemble fuel and oxidizer nanoparticles with a gas-generating binder into microscale particle composites. This approach results in reactivity enhancement of nanothermite systems by alleviating reactive sintering of the nanoparticle components due to rapid gasification. However, this method is not readily scalable and amenable to large-scale manufacturing due to its slow solution processing rates and the risks associated with the presence of high electric fields in the presence of electrostatic discharge-sensitive reactive materials. Here, we explore spray drying as an alternative approach to assemble Al/CuO nanoparticles into nitrocellulose (NC)-based mesoparticle composites and evaluate their energetic performance against physically mixed powders and electrosprayed mesoparticles. The spray dried mesoparticles show ∼2–7-fold higher pressurization rates and shorter burn times than their physically mixed counterparts and follow a similar trend with electrospray. The higher reactivity of the mesoparticles is attributed to rapid gas generation and reduced sintering from the decomposition of the NC binder. We further demonstrate that spray drying generates mesoparticles with size (∼1.5–4 μm), morphology, and reactivity enhancement similar to that from the electrospray method, while achieving remarkably high production rates (as high as ∼275 g h−1). Thus, this work presents spray drying as a highly scalable strategy to achieve reactivity enhancement and processability, thereby enabling high-yield manufacturing of energetic materials, which is a prelude to what might evolve into 3-D printing approaches for propellants. [ABSTRACT FROM AUTHOR]

The neutralization of biologics used as components in weapon systems poses a considerable challenge. One strategy is to deliver both heat and biocidal agents simultaneously. In this paper we employ an electrospray assembly approach to create Al/CuO nanothermite microparticles containing molecular iodine ranging from 5 wt.% to 50 wt.%, and evaluate their combustion properties and potential use as sporicidal agents. The reactivity was evaluated using a constant-volume combustion cell, which showed that, with increasing iodine content, the Al/CuO/I 2 reaction rate is decreased by several orders of magnitude, while the burning time increased. Results also show that the reactivity of the composites can be increased by reducing the particle loading in the precursor. The post-combustion products are determined to be Al 2 O 3 , Cu and CuI. T-Jump (temperature jump) wire ignition experiments showed that the temperature for microparticles containing up to 20 wt.% of iodine are ∼750 °C, which is similar to the ignition temperature of Al/CuO composites. In-situ rapid heating SEM imaging of Al/CuO/I 2 composites confirmed that iodine was released (<500 °C) prior to the thermal reaction (∼800 °C). T-Jump time of flight mass spectrometry showed an early release of iodine starting at ∼300 °C, and a later release ∼670 °C corresponding to iodine that had been stabilized in the alumina shell of the aluminum nanoparticles during preparation of the electrospray precursor solution. The results conclude that iodine loadings of up to 50 wt.% can be stabilized within the microparticle to allow for a higher temperature iodine release along with the high temperature thermite reaction making this material a strong candidate to be used in biocidal applications. [ABSTRACT FROM AUTHOR]

Whileultrafine metal particles offer the possibility of very highenergy density fuels, there is considerable uncertainty in the mechanismby which metal nanoparticles burn, and few studies that have examinedthe size dependence to their kinetics at the nanoscale. In this workwe quantify the size dependence to the burning rate of titanium andzirconium nanoparticles. Nanoparticles in the range of 20–150nm were produced via pulsed laser ablation, and then in-flight size-selectedusing differential electrical mobility. The size-selected oxide freemetal particles were directly injected into the post flame regionof a laminar flame to create a high temperature (1700–2500K) oxidizing environment. The reaction was monitored using high-speedvideography by tracking the emission from individual nanoparticles.We find that sintering occurs prior to significant reaction, and thatonce sintering is accounted for, the rate of combustion follows anear nearly (diameter)1power-law dependence.Additionally, Arrhenius parameters for the combustion of these nanoparticleswere evaluated by measuring the burn times at different ambient temperatures.The optical emission from combustion was also used to model the oxidationprocess, which we find can be reasonably described with a kineticallycontrolled shrinking core model. [ABSTRACT FROM AUTHOR]

An electrospray–differentialmobility analyzer (ES-DMA)was operated with an aerosol flow-mode, temperature-programmed approachto enhance its ability to characterize the particle size distributions(PSDs) of nanoscale particles (NPs) in the presence of adsorbed andfree ligands. Titanium dioxide NPs (TiO2-NPs) stabilizedby citric acid (CA) or bovine serum albumin (BSA) were utilized asrepresentative systems. Transmission electron microscopy (TEM) andinductively coupled plasma mass spectrometry were used to providevisual information and elemental-based PSDs, respectively. Resultsshow that the interference resulting from electrospray-dried nonvolatilesalt residual nanoscale particles (S-NPs) could be effectively reducedusing the thermal treatment process: PSDs were accurately measuredat temperatures above 200 °C for CA-stabilized TiO2-NPs and above 400 °C for BSA-stabilized TiO2-NPs.Moreover, TEM confirmed the volumetric shrinkage of S-NPs due to thermaltreatment and also showed that the primary structure of TiO2-NPs was relatively stable over the temperature range studied (i.e.,below 700 °C). Conversely, the shape factor for TiO2-NPs decreased after treatment above 500 °C, possibly due toa change in the secondary (aggregate) structure. S-NPs from BSA-stabilizedTiO2-NPs exhibited higher global activation energies towardinduced volumetric shrinkage than those of CA-stabilized TiO2-NPs, suggesting that activation energy is dependent on ligand size.This prototype study demonstrates the efficacy of using ES-DMA coupledwith thermal treatment for characterizing the physical state of NPs,even in a complex medium (e.g., containing plasma proteins) and inthe presence of particle agglomerates induced by interaction withbinding ligands. [ABSTRACT FROM AUTHOR]

Although electrospray-differential mobility analyzers (ES-DMA) have been previously employed to characterize ligand binding to nanoparticles, absolute quantification of surface coverage can be inaccurate at times because of ligand conformational effects. In this Letter, we report a quantitative technique by in-flight coupling of a particle mass analyzer (APM) with ES-DMA, thus enabling a direct quantitative analysis of mass independent of particle size, material, morphology and conformation. We demonstrate the utility of ES-DMA-APM by studying two model complex systems (gold nanoparticle-bovine serum albumin and polystyrene bead-antibody) as a function of concentration and pH. Our results obtained with ES-DMA-APM are in excellent agreement with prior work. We anticipate that this will enhance the capabilities of online quantitative characterization of ligand binding to nanoparticles [ABSTRACT FROM AUTHOR]

Abstract: The technique of electrospray differential mobility analysis (ES-DMA) was examined as a potential potency assay for routine virus particle analysis in biomanufacturing environments (e.g., evaluation of vaccines and gene delivery products for lot release) in the context of the International Committee of Harmonisation (ICH) Q2 guidelines. ES-DMA is a rapid particle sizing method capable of characterizing certain aspects of the structure (such as capsid proteins) and obtaining complete size distributions of viruses and virus-like particles. It was shown that ES-DMA can distinguish intact virus particles from degraded particles and measure the concentration of virus particles when calibrated with nanoparticles of known concentration. The technique has a measurement uncertainty of ≈20%, is linear over nearly 3 orders of magnitude, and has a lower limit of detection of ≈109 particles/mL. This quantitative assay was demonstrated for non-enveloped viruses. It is expected that ES-DMA will be a useful method for applications involving production and quality control of vaccines and gene therapy vectors for human use. [Copyright &y& Elsevier]

We demonstrate a high-resolution in situ experimental method for performing simultaneous size classification and characterization of functional gold nano-particle clusters (GNCs) based on asymmetric-flow field flow fractionation (AFFF). Field emission scanning electron microscopy, atomic force microscopy, multi-angle light scattering (MALS), and in situ ultraviolet-visible optical spectroscopy provide complementary data and imagery confirming the cluster state (e.g., dimer, trimer, tetramer), packing structure, and purity of fractionated populations. An orthogonal analysis of GNC size distributions is obtained using electrospray-differential mobility analysis (ES-DMA). We find a linear correlation between the normalized MALS intensity (measured during AFFF elution) and the corresponding number concentration (measured by ES-DMA), establishing the capacity for AEFF to quantify the absolute number concentration of GNCs. The results and corresponding methodology summarized here provide the proof of concept for general applications involving the formation, isolation, and in situ analysis of both functional and adventitious nanoparticle clusters of finite size. [ABSTRACT FROM AUTHOR]

Abstract: Mesoporous silica nanoparticles (MSN) have potential as drug delivery and controlled release devices due to their high surface area and absorption capabilities. The effect of surface charge and pH on the release of the fluorescent dye, rhodamine 6G, from MSN has been studied. Release profiles of rhodamine 6G from bare and amine-coated MSN at pH 5.0 and 7.4 are very different and demonstrate that electrostatic interactions between entrapped rhodamine 6G molecules and the charged surface of the MSN have a significant effect on release kinetics. Release of rhodamine 6G from amine-coated MSN can be fit to a single exponential function, while release from bare MSN can be fit to a double exponential function—indicating that the release of rhodamine 6G from bare MSN is a two-phase process. In addition, it was determined that MSN need to be sonicated in dye solution to maximize their loading capacity. [Copyright &y& Elsevier]

The technique of high-temperature oxidation tandem differential mobility analysis has been applied to the study of diesel nanoparticle oxidation. The oxidation rates in air of diesel nanoparticles sampled directly from the exhaust stream of a medium-duty diesel engine were measured over the temperature range of 800-1140 °C using online aerosol techniques. Three particle sizes (40, 90, and 130 nm mobility diameter) generated under engine load conditions of 10, 50, and 75% were investigated. The results show significant differences in the behavior of the 10% load particles as compared to the 50 and 75% load particles. The 10% load particles show greater size decrease at temperatures below 500 °C and significant size decrease at temperatures between 500 and 1000 °C in a non-oxidative environment, indicating release of adsorbed volatile material or thermally induced rearrangement of the agglomerate structure. Activation energies determined are 114, 109, and 108 kJ tool[sup -1] for the 10, 50, and 75% load particles, respectively. These activation energies are lower than for flame soot (Higgins et al. J. Phys. Chem. A 2002, 106, 96), but the preexponential factors are lower by 3 orders of magnitude, and the overall oxidation rates are slower by up to a factor of 4 over the temperature range studied. Possible reasons for the differences are discussed in the text. [ABSTRACT FROM AUTHOR]

[Display omitted] • Plasma-synthesized amorphous Si NPs (a -nSi) incorporate abundant hydrogen. • The reactivity of a -nSi/KClO 4 increases by a factor of six compared with nAl. • The energetic performance of nSi is correlated with its hydrogen content. • In situ release of hydrogen from hydrides enhances the reactivity. In this work, we utilize a low-temperature non-equilibrium plasma to nucleate and grow sub-10 nm Si particles with varying degrees of crystallinity by tuning the level of power coupled into plasma discharge. Temperature-programmed desorption spectroscopy shows that as-prepared amorphous Si nanoparticles (a -nSi) incorporate more hydrogen than crystalline Si nanoparticles (c -nSi). Further, hydrogen is incorporated in the material in the form of higher silicon hydrides with a lower desorption temperature. Combustion cell measurements show that when formulated with KClO 4 , a -nSi outperforms its crystalline counterpart with respect to pressure output. The pressurization rate of a -nSi/KClO 4 composite increases by a factor of six compared with nAl to 0.66 MPa·μs−1. Evidence of hydrogen release (∼730 K) from Temperature-jump time-of-flight mass spectrometry (T-Jump TOFMS) of a -nSi/KClO 4 suggests the creation of Si dangling bonds prior to ignition (∼820 K), which then react exothermically with oxygen liberated from KClO 4 , leading to ignition. Explosive reaction of H 2 /O 2 mixture likely contributes to the rapid pressure rise. The enhanced energetic performance of hydrogenated a -nSi compared to its crystalline counterpart suggests that incorporation of hydrogen is a promising strategy for improving the performance of nanoenergetic materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Focused microwave ignition of Ti nanoparticles printed in PVDF matrix. • Ti nanoparticles served the dual function as a fuel and a microwave susceptor. • Power-dependent and independent regimes were found. • Dielectric properties control ignition in power-dependent regime. • Combustion reaction kinetics control ignition in power saturation region. One of the challenges in propellant formulation is the inability to moderate the burn rate dynamically. Here, we consider spatially localized remote ignition of additively manufactured composites via microwave absorption. Previous studies demonstrated that a passivating shell on Ti nanoparticles (nTi) enhances microwave absorption. Incorporated within a polyvinylidene fluoride (PVDF) matrix, Ti/PVDF films ignite under microwave irradiation in air. To gain more comprehensive insight into pre-ignition behavior, the ignition delay was studied as a function of applied power and the microwave susceptor loading. Infrared (IR) camera studies were further used to investigate the heating behavior of the films under variable power. We found that ignition delay decreases with increasing power to an apparent heating saturation region, where the ignition sensitivity is limited by the combustion reaction kinetics. Thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC) showed that nTi oxidizes with O 2 at lower temperatures than fluorination with PVDF and drives combustion. Findings in this work build a pathway for remote and controlled ignition of solid propellants via microwave radiation. [ABSTRACT FROM AUTHOR]

• The combustion behavior and ignition mechanism of several Si-based thermites were investigated. • The incorporation of Ti nanoparticles reduced the ignition temperature of Si/KClO 4. • The enhanced reactivity of Si/KClO 4 has been shown via adding Ti nanoparticles. • The combustion efficiency of Si/Ti/KClO 4 has been improved compared to Si/KClO 4. This work explores the ignition mechanism of silicon (Si) based thermites, and it is supposed that the phase change of silica (SiO 2) coating on the Si core producing fractures may play a crucial role in the ignition of Si-based thermites. Several Si-based thermites were evaluated by the combustion test and calorimeter, and potassium perchlorate (KClO 4) is turned out to be a promising oxidizer given the high reactivity and considerable heat release. Titanium (Ti) nanoparticles with a lower onset oxidization temperature than Si were incorporated into Si/KClO 4 system via a facile sonicating method. The ignition temperature of Si/KClO 4 has reduced markedly by ~80–130 °C with significant increases of ~5-8x in pressurization rate and decreases by a factor of ~2–3 in burn time when adding 30–70% Ti by mole into the fuel. The combustion efficiency is improved dramatically from ~59% to ~73%. The enhanced combustion performance could be attributed to the lower ignition temperature of Ti/KClO 4 leading to the initiation reaction of the ternary composites, thus promoting energy release and the reactivity of the ternary system. This work not only investigates the ignition mechanism of Si-based thermites but also sets a stage for tuning the ignition and combustion of Si-based thermites via facile incorporation of Ti nanoparticles. [ABSTRACT FROM AUTHOR]