No description available.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 90-93). Also available via the Internet.

Thesis (Ph.D.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references.

Polyelectrolytes coated on high surface curvature nanoparticles (NPs) have been prepared and characterized by a variety of solid-state nuclear magnetic resonance (NMR) experiments in order to examine surface interactions, polymer-water association and polymer dynamic properties of layer components. Gold nanoparticles of four nanometers in diameter pre-stabilized by 4-dimethylaminopyridine (DMAP), and silica and neodymium NPs were chosen as substrates for these studies. The high surface to volume ratio provided by such nanoparticles is advantageous for NMR analysis, which requires a high material content for adequate sensitivity. Firstly, poly(styrene sulfonate) was deposited on gold NPs by electrostatic self-assembly where charged polyelectrolytes adsorb onto an oppositely charged substrate. Surface charges on gold NPs were provided by the ligand DMAP that induces a positive charge at the NP surface that is otherwise neutral. Nanoparticle encapsulation by PSS was monitored by the gold surface plasmon absorption band (SPB) which revealed a good stability under assembly conditions where the pH was maintained above the DMAPsoln pKa and for a polymer radius of gyration comparable to the particle radius. An electrostatic association between DMAPbound and PSS, rather than a ligand substitution, was detected by solid state 13C NMR. When a subsequent layer composed of a weak or a strong polycation was added, the stability of the bilayer was found to be dictated by the nature of the multiple, weak interactions of the polymer functional groups (SO3, NH2, N(CH 3)2+Cl-, NH3 +) with the gold surface relative to that of DMAPbound which in turn is influenced by the assembly pH. / A detailed study of the interactions between the polyelectrolytes, stabilizers and substrates was also extended to polyelectrolyte multilayers coated on gold NPs of different dimensions. Limitations in the application of the layer-by-layer self-assembly technique to very small NPs were investigated and strategies to optimize the method were proposed. 1H NMR analysis in the solid state and 2H NMR analysis in solution revealed that water association and film dynamics were closely related to the identity of the capping layer and independent of even/odd layer effects. These results were compared to those obtained for larger NP substrates which revealed many similarities between the two systems. / A study of the parameters that affect the fabrication of Poly(L-lysine) and DNA polyelectrolyte multilayer films was also conducted for both flat and highly curved surfaces. Such polyelectrolyte films coated on nanopartic1es can be considered as potential vectors for gene therapy. Control over DNA loading into films was performed by varying the ionic strength and pH of polyelectrolyte assembly solutions. DNA density, film degradability and transfection efficiency were examined to determine optimal conditions for vector preparation in gene therapy. Finally, the acid-base properties of lanthanide-based nanoparticles of 10 nm of diameter were explored under a wide range of pH conditions. The interactions of the neodymium oxide nanoparticles with the cationic poly(allylamine hydrochloride) and the anionic poly(styrene sulfonate) polymers were investigated by following spectroscopically optical changes in suspension absorbance and visual changes in NP dimensions. Transparancy and efficiency of stabilization were the evaluated criteria for polymers to be considered as potential stabilizing agents for neodymium oxide NPs used in neutrino detection experiments.

The kinetics and mechanism of the place exchange reaction(PER) of alkylthiols with alkylthiol-protected gold nanoparticles(AuNP) are investigated. Using chemically similar alkylthiols it was possible to study the reaction in the absence of perturbing factors, enabling detailed mechanistic and kinetic studies to be explored. It is found that the reactions are zero order in incoming ligand and overall follow a second order diffusion limited Langmuir rate law. In the case where there is little chemical distinction between the incoming and capping ligands, the reactions proceed to an endpoint consistent with a Keq=1. The rate of the reaction is dependent on the chain length of the capping ligand and the AuNP core size. The related dialkyldisulphide for-alkylthiol AuNP exchange reaction is consistent with the same rate law and also proceeds to a well-defined endpoint. However, the rate constant is 20-fold less than the alkylthiol case. These results lead to a convergent model of PERs where the rate limiting process involves both incoming and outgoing ligands, with diffusion of the incoming ligand to the AuNP surface as the major controlling factor of the reaction rate.

Thesis (Ph. D. in Chemical Engineering)--Vanderbilt University, May 2006. / Title from title screen. Includes bibliographical references.

Thesis (M.Eng.). / Written for the Dept. of Chemical Engineering. Title from title page of PDF (viewed 2009/06/15). Includes bibliographical references.

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The densification behavior of porous gold films made from commercial circuit paste used in microelectronic packaging applications was studied. Constrained gold circuit films of 60-65μm thick were formed by multiple screen printing of the gold paste on rigid alumina substrates, while freestanding films were obtained by carefully peeling off gold films from the substrates after binder burn-out. Optical techniques were developed to determine the densification kinetics of the constrained and freestanding films at temperatures below 1000°C. The densification kinetics of gold films constrained on rigid substrates were observed to be significantly retarded relative to the free films, at all sintering temperatures between 650°C and 900°C studied. SEM studies revealed the microstructure of the constrained films to be much more porous than its freestanding film counterpart. Considerably higher sintering temperatures were required to obtain densities comparable to those of freestanding films. SEM studies also showed no significant difference in grain size between the sintered freestanding and constrained gold films. Inplane tensile stresses generated during constrained-film sintering, was determined to have a maximum value of 460 KPa at the sintering temperature of 750°C. The negligible difference in grain size between the sintered freestanding and constrained gold films, and the small magnitude of the measured tensile stresses, were both determined to be insufficient to account for the observed retardation in the densification kinetics of the constrained gold films. The activation energies for densification of the porous gold films during isothermal sintering, were found to be 21.54±1.03 Kcal/mole and 45.12​​±1.6 Kcal/mole for freestanding and constrained gold films respectively. These values corresponded very well with the activation energies for grain-boundary diffusion and lattice diffusion respectively, for gold as found in literature. Hence from our results of the activation energies for densification of the constrained and freestanding gold films, coupled with our studies on grain growth and stress, we suggest that the observed retardation in the densification kinetics of the constrained gold films are due to a change in the dominant diffusion mechanism during sintering of the porous gold films constrained on rigid substrates. / Master of Science