| The recent worldwide interest in nanotechnology spans a wide variety of scientific fields such as electronics, biology, materials science and medicine. Because of their extremely small dimensions, nanoparticles demonstrate properties different from matter at larger scales. Understanding these unusual properties and utilizing them for macroscale devices is an overall goal for nanotechnology. Moreover, manipulating these small particles into organized structures is crucial for taking full advantage of what nanotechnology has to offer, however it has proven to be a difficult task. Recent work utilizing electrostatic forces shows great potential for the self-assembly of nanoparticles into organized two-dimensional and three-dimensional structures. Overall, this work examines how nanotechnology and self-assembly can benefit the field of energetic materials.;Because of aluminum's high energy density and low cost, it has been used in the field of energetic materials for several decades. In order to achieve sufficient energy release rates, aluminum is typically manufactured as a powder having spherical particles with diameters on the micron scale. It is well-known that decreasing the original particle diameter of a fuel particle will increase the burning time and, thus, energy release rate. Therefore, aluminum particles have recently been made to have diameters on the nanoscale, and shown to be advantageous for several applications. The combustion of nanoaluminum (nAl) in various systems is the primary focus of this study. A progression of experiments is used to analyze the combustion of nAl: (1) a fully heterogeneous flame spread system, (2) a semi-homogeneous sonicated thermite system and (3) a quasi-homogeneous self-assembled thermite system.;The flame spread experiment physically separates the nAl from the gaseous oxidizer allowing for a well-understood convective, diffusive, reactive system to be analyzed. Because of the simplicity of the experimental setup, variables are easily changed and their effects on the flame spread rate are observed. Overall, spread rates are 2 to 3 orders of magnitude greater than what is demonstrated with typical solid fuels due to the high reactivity of the nAl. This large difference in spread rate brings about a fingering combustion instability in normal gravity conditions that has only been shown to occur in microgravity conditions. Moreover, a stability map is created based on the nondimensional Lewis and Damkohler numbers that predicts when a continuous flame front will transition to a fingering instability. This, along with the various other trends, is predicted using a simple scaling analysis.;A nanoscale thermite is created via sonication of nAl and nanocopper-oxide (nCuO) particles. Although the mixture is unorganized and random, these materials boast extremely exothermic reactions with propagation rates on the order of 1 km/s. Experiments are performed to examine the effect of adding a diluent to the system. Two types of materials are added, a stable end product, aluminum-oxide, and long alkyl chain hydrocarbons. Both materials severely hinder the propagation rate, however, experiments suggest that hydrocarbon addition could help with the material's sensitivity to electrostatic discharge. Equilibrium calculations suggest that a dual temperature and gas production criteria must be met to allow for the convective propagation mechanism to take place and fast propagation rates to occur. Because of the hydrocarbons required for self-assembly, these experiments also give an indication of how the self-assembled material will react.;To electrostatically self-assemble a nAl/nCuO thermite, the constituents are first coated with an o-functionalized alkyl chain ligand and suspended in a separate solutions. Upon mixing, the opposite electrostatic charges agglomerate the two constituents, which subsequently precipitate out of solution. Analyzing the material with Scanning Electron Microscopy shows that a portion has self-assembled into microspheres having diameters from 1-5mum. This is the first known energetic nanocomposite built with a bottom-up engineering approach. The combustion properties of the self-assembled material are compared to that of the sonicated material, with similar amounts of added hydrocarbons. The propagation in microchannels is examined. Unlike the sonicated material, the self-assembled material is able to achieve ignition and propagate the full length of the microchannel. This gives indication that electrostatic self-assembly is a viable method for building energetic materials from the bottom-up, and could potentially increase the intimacy of the mixing. |
