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Metal combustion reaction is highly exothermic and is used in energetic applications, such as propulsion, pyrotechnics, powering micro-and nano-devices, and nanomaterials synthesis. Aluminum (Al) is attracting great interest in those applications because of its high energy density, earth abundance, and low toxicity. Nevertheless, Al combustion is hard to initiate and progresses slowly and incompletely. On the other hand, ultrathin carbon nanomaterials, such as graphene, graphene oxide (GO), and graphene fluoride (GF), can also undergo exothermic reactions. Herein, we demonstrate that the mixture of GO and GF significantly improves the performance of Al combustion as interactions between GO and GF provide heat and radicals to accelerate Al oxidation. Our experiments and reactive molecular dynamics simulation reveal that GO and GF have strong chemical and thermal couplings through radical reactions and heat released from their oxidation reactions. GO facilitates the dissociation of GF, and GF accelerates the disproportionation and oxidation of GO. When the mixture of GO and GF is added to micron-sized Al particles, their synergistic couplings generate reactive oxidative species, such as CFx and CFxOy, and heat, which greatly accelerates Al combustion. This work demonstrates a new area of using synergistic couplings between ultrathin carbon nanomaterials to accelerate metal combustion and potentially oxidation reactions of other materials.

Silver-containing oxidizers are of interest as biocidal components in energetic application such as thermites due to their biocidal agent delivery. In this study, AgFeO2, was evaluated as an oxidizer in aluminum-based thermite system. This novel oxidizer AgFeO2 particles were prepared via a wet-chemistry method and its structure, morphologies and thermal behavior were investigated using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and differential scanning calorimetry, and time-resolved temperature-jump time-of-flight mass spectrometry. The results indicate the decomposition pathways of AgFeO2 vary with heating rates from a two-step at low heating rate to a single step at high heating rate. Ignition of Al/AgFeO2 occurs at a temperature just above the oxygen release temperature that is very similar to Al/Fe2O3 and Al/CuO. However, with a pressurization rate three times of Al/CuO, Al/AgFeO2 yields a comparable result as to Al/hollow-CuO or Al/KClO4/CuO, with a simpler preparation method. The post combustion products demonstrated that the Al/AgFeO2 thermite reaction produces a fine dispersion of elemental nanosized silver particles which coats the larger alumina particles and is thus bioavailable.

Silver-containing oxidizers are of interest as biocidal components in energetic application such as thermites due to their biocidal agent delivery. In this study, AgFeO2, was evaluated as an oxidizer in aluminum-based thermite system. This novel oxidizer AgFeO2 particles were prepared via a wet-chemistry method and its structure, morphologies and thermal behavior were investigated using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and differential scanning calorimetry, and time-resolved temperature-jump time-of-flight mass spectrometry. The results indicate the decomposition pathways of AgFeO2 vary with heating rates from a two-step at low heating rate to a single step at high heating rate. Ignition of Al/AgFeO2 occurs at a temperature just above the oxygen release temperature that is very similar to Al/Fe2O3 and Al/CuO. However, with a pressurization rate three times of Al/CuO, Al/AgFeO2 yields a comparable result as to Al/hollow-CuO or Al/KClO4/CuO, with a simpler preparation method. The post combustion products demonstrated that the Al/AgFeO2 thermite reaction produces a fine dispersion of elemental nanosized silver particles which coats the larger alumina particles and is thus bioavailable.

A fast, quantitative method for determining the dimensions of nanorods (i.e., length and diameter) is described, based on hyphenation of differential mobility analysis (DMA) with single particle inductively coupled plasma mass spectrometry (spICP-MS). Seven gold nanorod samples with different dimensions (diameters 11.8 nm to 38.2 nm, aspect ratios 1.8 to 6.9) were used to validate the method. We demonstrate that DMA-spICP-MS can (1) achieve quantification of both length and diameter comparable with TEM analysis, (2) make statistically meaningful measurements in minutes at low concentrations (<108 mL-1) and (3) separate nanorods from spheres and quantify the geometry of each population. A robustness analysis of this method was performed to evaluate potential biases in this approach.

Cisplatin-complexed gold nanoparticles (PtII-AuNP) provide a promising strategy for chemo-radiation-based anticancer drugs. Effective design of such platforms necessitates reliable assessment of surface engineering on a quantitative basis and its influence on drug payload, stability, and release. In this paper, poly(ethylene glycol) (PEG)-stabilized PtII-AuNP was synthesized as a model antitumor drug platform, where PtII is attached via a carboxyl-terminated dendron ligand. Surface modification by PEG and its influence on drug loading, colloidal stability, and drug release were assessed. Complexation with PtII significantly degrades colloidal stability of the conjugate; however, PEGylation provides substantial improvement of stability in conjunction with an insignificant trade-off in drug loading capacity compared with the non-PEGylated control (<20% decrease in loading capacity). In this context, the effect of varying PEG concentration and molar mass was investigated. On a quantitative basis, the extent of PEGylation was characterized and its influence on dispersion stability and drug load was examined using electrospray differential mobility analysis (ES-DMA) hyphenated with inductively coupled plasma mass spectrometry (ICP-MS) and compared with attenuated total reflectance-FTIR. Using ES-DMA-ICP-MS, AuNP conjugates were size-classified based on their electrical mobility, while PtII loading was simultaneously quantified by determination of Pt mass. Colloidal stability was quantitatively evaluated in biologically relevant media. Finally, the pH-dependent PtII release performance was evaluated. We observed 9% and 16% PtII release at drug loadings of 0.5 and 1.9 PtII/nm2, respectively. The relative molar mass of PEG had no significant influence on PtII uptake or release performance, while PEGylation substantially improved the colloidal stability of the conjugate. Notably, the PtII release over 10 days (examined at 0.5 PtII/nm2 drug loading) remained constant for n

The combustion mechanism of [AlCp*]4 (Cp* = pentamethylcyclopentadienyl), a ligated aluminum(I) cluster, was studied by a combination of experimental and theoretical methods. Two complementary experimental methods, temperature-programmed reaction and T-jump time-of-flight mass spectrometry, were used to investigate the decomposition behaviors of [AlCp*]4 in both anaerobic and oxidative environments, revealing AlCp* and Al2OCp* to be the major decomposition products. The observed product distribution and reaction pathways are consistent with the prediction from molecular dynamics simulations and static density functional theory calculations. These studies demonstrated that experiment and theory can indeed serve as complementary and predictive means to study the combustion behaviors of ligated aluminum clusters and may help in engineering stable compounds as candidates for rocket propellants.

Nanoparticles (NPs) dispersed within a conductive host are essential for a range of applications including electrochemical energy storage, catalysis, and energetic devices. However, manufacturing high quality NPs in an efficient manner remains a challenge, especially due to agglomeration during assembly processes. Here we report a rapid thermal shock method to in situ synthesize well-dispersed NPs on a conductive fiber matrix using metal precursor salts. The temperature of the carbon nanofibers (CNFs) coated with metal salts was ramped from room temperature to ∼2000 K in 5 ms, which corresponds to a rate of 400,000 K/s. Metal salts decompose rapidly at such high temperatures and nucleate into metallic nanoparticles during the rapid cooling step (cooling rate of ∼100,000 K/s). The high temperature duration plays a critical role in the size and distribution of the nanoparticles: the faster the process is, the smaller the nanoparticles are, and the narrower the size distribution is. We also demonstrated that the peak temperature of thermal shock can reach ∼3000 K, much higher than the decomposition temperature of many salts, which ensures the possibility of synthesizing various types of nanoparticles. This universal, in situ, high temperature thermal shock method offers considerable potential for the bulk synthesis of unagglomerated nanoparticles stabilized within a matrix.

Nanoparticles (NPs) dispersed within a conductive host are essential for a range of applications including electrochemical energy storage, catalysis, and energetic devices. However, manufacturing high quality NPs in an efficient manner remains a challenge, especially due to agglomeration during assembly processes. Here we report a rapid thermal shock method to in situ synthesize well-dispersed NPs on a conductive fiber matrix using metal precursor salts. The temperature of the carbon nanofibers (CNFs) coated with metal salts was ramped from room temperature to ∼2000 K in 5 ms, which corresponds to a rate of 400,000 K/s. Metal salts decompose rapidly at such high temperatures and nucleate into metallic nanoparticles during the rapid cooling step (cooling rate of ∼100,000 K/s). The high temperature duration plays a critical role in the size and distribution of the nanoparticles: the faster the process is, the smaller the nanoparticles are, and the narrower the size distribution is. We also demonstrated that the peak temperature of thermal shock can reach ∼3000 K, much higher than the decomposition temperature of many salts, which ensures the possibility of synthesizing various types of nanoparticles. This universal, in situ, high temperature thermal shock method offers considerable potential for the bulk synthesis of unagglomerated nanoparticles stabilized within a matrix.

Nanoparticles hosted in conductive matrices are ubiquitous in electrochemical energy storage, catalysis and energetic devices. However, agglomeration and surface oxidation remain as two major challenges towards their ultimate utility, especially for highly reactive materials. Here we report uniformly distributed nanoparticles with diameters around 10 nm can be self-assembled within a reduced graphene oxide matrix in 10 ms. Microsized particles in reduced graphene oxide are Joule heated to high temperature (∼1,700 K) and rapidly quenched to preserve the resultant nano-architecture. A possible formation mechanism is that microsized particles melt under high temperature, are separated by defects in reduced graphene oxide and self-assemble into nanoparticles on cooling. The ultra-fast manufacturing approach can be applied to a wide range of materials, including aluminium, silicon, tin and so on. One unique application of this technique is the stabilization of aluminium nanoparticles in reduced graphene oxide film, which we demonstrate to have excellent performance as a switchable energetic material.

Nanoparticles hosted in conductive matrices are ubiquitous in electrochemical energy storage, catalysis and energetic devices. However, agglomeration and surface oxidation remain as two major challenges towards their ultimate utility, especially for highly reactive materials. Here we report uniformly distributed nanoparticles with diameters around 10 nm can be self-assembled within a reduced graphene oxide matrix in 10 ms. Microsized particles in reduced graphene oxide are Joule heated to high temperature (∼1,700 K) and rapidly quenched to preserve the resultant nano-architecture. A possible formation mechanism is that microsized particles melt under high temperature, are separated by defects in reduced graphene oxide and self-assemble into nanoparticles on cooling. The ultra-fast manufacturing approach can be applied to a wide range of materials, including aluminium, silicon, tin and so on. One unique application of this technique is the stabilization of aluminium nanoparticles in reduced graphene oxide film, which we demonstrate to have excellent performance as a switchable energetic material.

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 (1000000 10 to the 11th power 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 +- 50K, 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., Published in Journal of Applied Physics, v115 p084903-1/084903-6, 2014

Nanometallic fuels suffer from processing challenges that have significantly retarded their utility, primarily because their very high surface area/small particle size increases the viscosity of the polymer binder and oxidizer mix, such that high mass fractions of fuel cannot be formulated. The other concern is that they lose surface area rapidly, on a time-scale commensurate with combustion. We employ electrospray as a means to create a gel within a droplet by evaporation induced rapid aggregation of aluminum and oxidizer nanoparticles containing a small mass fraction of an energetic binder. We find that the average size of the microparticles can be systematically changed from 2 microns to 16 microns. The combustion behavior is found to be very different from either nanoaluminum or micron aluminum and their corresponding thermite mixtures. The material which is super-micron sized has surface area consistent with the nanoparticle comprising it and the binder serves to act as a gas generator to minimize sintering., Presented at the 52nd Aerospace Sciences Meeting, 13-17 January 2014, National Harbor, Maryland.

With the recent implementation of nano sized metal powders into energetic composites such as solid rocket propellants, incorporating metal nanoparticles with high mass loading in the propellant has become an issue. In this work, an electrospray deposition technique was employed to increase particle loading of nano aluminum (n-Al) and demonstrate the potential of the fluoropolymer, polyvinylidene fluoride (PVDF), as an energetic binder. A mass percentage of 50% n-Al in PVDF was determined to have the optimal combustion qualities when ignited in air. The Al/PVDF energetic nanocomposite film morphologies were analyzed using scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Combustion characteristics of the film were analyzed using thermogravimetric analysis/mass spectrometry (TGA/MS) and temperature jump time of flight mass spectrometry (T-jump TOFMS). Ignition temperatures were determined at various pressured in air and argon environments., Presented at AIAA SciTech, 52nd Aerospace Sciences Meeting, National Harbor, MD, 13-17 Jan 2014.

The basic objective of this program is to explore new architectures for energetic materials, and to use novel diagnostic tools that probe the underlying nature of reactivity of this class of materials. The specific objective of this program are two fold. A. Development of novel architectures for reactive metals. B. Characterization of nanoparticle reactivity, and development of scaling laws from novel measurements of reactivity using a new concept in mass spectrometry (T-Jump Mass Spectrometry; TJMS), The original document contains color images.

Many biological and physical objects derive their unique properties through an integrated multilength scale organization of their constituent nano and microscale structures. Such multiscaled structures are being exploited to engineer devices such as adhesives mimicking spatulae of a gecko, porous silicon drug delivery systems, to adaptive porous materials that mimick the multifunctionality of bone. A common feature in all these structures is that nanoscale units are all integrated into micron to macro scale structures and are accessible as individual modules for rapid response. Such design principles are crucial to the goals of our proposed work., Presented at the 2012 Joint Office of Naval Research (ONR)/Air Force Office of Scientific Research Advanced Energetic Materials Program Review, 7-10 August 2012. Contains series of briefings: Overview; Metallic Clusters, Mesoscopic Aggregates and their Reactive Characterization, Bryan Eichhorn and Michael R. Zachariah (p19); Graphene as a Reactive Material and Carrier of Energetic Materials, I. A. Aksay, A. Selloni, R. Car, D. M. Dabbs (43); and Integration of Nanoenergetic Composite Ingredients/Mixtures and Reaction Characterization, R. A. Yetter, S. F. Son, S. Thynell and L. J. Groven (p65).

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 ≈10(9)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.

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 ≈10(9)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.

Using the classical molecular dynamics method we simulate the mechanochemical behavior of small, core diameter <10 nm oxide coated aluminum nanoparticles. Aluminum nanoparticles with core diameters of approximately 5 and 8 nm are simulated with 1 and 2 nm thick oxide coatings or shells. In addition to thickness the shells are parametrized by varying degrees of crystallinity, density, and atomic ratios in order to study their effect on the ignition of nanoparticle oxidation. The oxide shells are parametrized to consider oxide coatings with the defects that commonly occur during the formation of an oxide layer and for comparison with a defect free crystalline oxide shell. Computed results include the diffusion coefficients of aluminum cations for each shell configuration and over a range of temperatures. The observed results are discussed and compared with the ignition mechanisms reported in the literature. From this effort we have found that the oxidation ignition mechanism for nanometer sized oxide coated aluminum particles is the result of an enhanced transport due to a built-in electric field induced by the oxide shell. This is in contrast to the currently assumed pressure driven diffusion process. This induced electric field accounts for approximately 90% of the mass flux of aluminum ions through the oxide shell. The computed electric fields show good agreement with published theoretical and experimental results., Published in Journal of Applied Physics, v107 n2 p024901-1/024901-9, 2010.

The focus of this work is to understand quantitatively, the nature of the reactivity of nanoparticles and nanocomposites for energetic materials application. Our approach takes two thrusts. 1. Single Particle Kinetics 2. Ensemble Fuel/Oxide Nanocomposite Kinetics., The original document contains color images.

Molecular dynamics simulations are used to probe the structure and stability of alkanethiolate self-assembled monolayers (SAMs) on gold nanoparticles. We have observed that the surface of gold nanoparticles becomes highly corrugated by the adsorption of the SAMs. Furthermore, as the temperature is increased, the SAMs dissolve into the gold nanoparticle, creating a liquid mixture at temperatures much lower than the melting temperature of the gold nanoparticle. By analyzing the mechanical and chemical properties of gold nanoparticles at temperatures below the melting point of gold, with different SAM chain lengths and surface coverage properties, we have determined that the system is metastable. The model and computational results that provide support for this hypothesis are presented., Prepared in collaboration with The original document contains color images.

In order to utilize the novel electrical, magnetic, optical, and physical properties of coated metal nanoparticles, one must be able to efficiently predict the nanoparticle size-dependent properties and to fabricate consistently sized nanoparticles. Both of these goals can be obtained through the use of numerical simulation. In this work the gold nanoparticle and nanoparticle/self-assembled monolayer systems have been analyzed with a physically accurate and computationally efficient numerical simulation. The simulation model and method are described in the following paper., See also ADM002075. Presented at the Army Science Conference (25th) held in Orlando, FL on 27-30 November 2006. The original document contains color images.