A key challenge for modern chemistry is the production of mesoscopic complexity and hierarchical order to ultimately bridge the gap between the molecular world and functional microdevices. As proof of concept, nature shows unambiguously that this approach can be rewarding. In particular, natural biominerals such as nacre, bone, and tooth enamel, consist of ordinary nanoscale components, yet assemble complex polycrystalline materials that are clearly superior to their synthetic counterparts. In this context, an exciting model system for biomimetic crystallization is the assembly of biomorphs by the co-precipitation of silica and metal carbonates. Despite being formed by purely inorganic processes, these structures show "life-like" morphologies such as twisted helices and cardioid leaves. At the nanoscale, silica-carbonate biomorphs consist of crystalline nanorods that assemble hierarchical architectures reminiscent of natural biominerals. In this research work, we improve the level of control over the growth process and quantitatively characterize the biomorph structures beyond simple qualitative observations. We report the synthesis of silica-carbonate biomorphs in single-phase, gradient-free solutions that differ markedly from the typical solution-gas or gel-solution setups. Our experimental approach reveals novel biomorph structural motifs, reduces transients in the chemical conditions, and expands the upper pH limit for biomorph formation to over 12 where silica is essentially soluble. Moreover, the single-phase approach significantly increases the duration of growth to assemble biomorph networks that extend to several millimeters. These unusually long biomorphs allow the first quantitative measurements of mesoscopic parameters such as the helix wavelength, period, width, and linear as well as tangential growth velocities. We find that the latter quantities are system-specific and tightly conserved during many hours of growth. We also systematically characterize the biomorph sheets and report the existence of an additional level of self-organization that creates oscillatory height variations along the sheet surface. These topographic features take the form of either concentric rings or disordered, patchy patterns with a wavelength of approximately 6.5 μm that shows no pronounced dependence on the reactant concentrations. These undulations are accompanied by a systematic out-of-plane displacement of the nanorods. Our results are discussed in the context of an earlier hypothesis that predicts pH oscillations near the crystallization front. We further investigate the effect of inorganic dopants that influence the morphological, compositional, and crystallographic properties of biomorphs. In the case of Pb²⁺ and Ag⁺ ions, biomorph growth is disrupted by the formation of competing precipitates. Similarly, the addition of Ca²⁺, Mg²⁺, and Zn²⁺ induces the rapid crystallization of witherite or amorphous silica-carbonate aggregates at enhanced growth rates. By comparison, the addition of strontium ions results in the assembly of classic biomorphs such as cardioid sheets and helices. Another aspect of the project lies at the overlap between geochemistry, paleontology, and astrobiology. To date, these fascinating biomorph microstructures have only been synthesized using model laboratory solutions. We report that mineral self-assembly can be also obtained from natural alkaline silica-rich water deriving from serpentinization. Specifically, we obtain water samples from the Ney springs in California and demonstrate the self-assembly of nanocrystalline biomorphs of barium carbonate and silica, as well as the formation mesocrystals and crystal aggregates of calcium carbonate with complex biomimetic textures. Our results suggest that silica-induced mineral self-assembly could have been a common phenomenon in alkaline environments of the early Earth and Earth-like planets. Moreover, the structural complexity obtained from these simple crystallization reactions in the natural Ney water further blurs the boundaries between geochemical and biological microscale morphologies that not too long ago were perceived as sharp and well-defined. / A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the Doctor of Philosophy. / Fall Semester 2016. / November 17, 2016. / Biomimetics, Biomorph, Crystallization, Hierarchical, Self-organization, Silica / Includes bibliographical references. / Oliver Steinbock, Professor Directing Dissertation; Richard Bertram, University Representative; Ken L. Knappenberger, Committee Member; Hedi Mattoussi, Committee Member.

Microwave chemistry has long been a subject of interest in both the organic and inorganic synthesis communities. Microwave heating has the potential to become a powerful force for green synthesis in industry as it uses much less power to accomplish the same goals, but a lack of understanding in how to translate traditional convective reactions into microwave reactions is hampering this progress. In this manuscript an overview of microwave physics and mathematics is given first. Then the role of microwave source and choice of microwave reaction vessel, along with precursor and solvent choice in the design of a microwave chemical reaction is explored. Next, synthesis of nickel and gold nanoparticles—chosen because of their ubiquitous nature in the literature—in a microwave is explored, and the kinetics examined. Additionally, the role of size dependent properties of the nanoparticles, as well as the role of the oxide layer on the nanoparticle, are explored in relationship to how the reaction heats in a standard laboratory microwave. Lastly, the role of power and frequency of the microwave radiation in the synthesis of nickel nanoparticles is examined, and relationships between the kinetics of the synthesis and the applied power and frequency of the microwave is extracted. / A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2017. / November 15, 2017. / microwave, nanoparticle, physical chemistry / Includes bibliographical references. / Geoffrey F. Strouse, Professor Directing Dissertation; Stephen Hill, University Representative; Albert E. Stiegman, Committee Member; Michael Shatruk, Committee Member.

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Thesis (Ph. D.)--University of North Texas, August, 2008. / Title from title page display. Includes bibliographical references.

published_or_final_version / Chemistry / Master / Master of Science

The aim of this dissertation has been to investigate the third order nonlinear susceptibility dispersion of molecules and polymers in order to estimate their purely electronic nonlinear response and in particular their optical Kerr nonlinear susceptibility in the 1 to 2 μm infrared spectral region. We have been successful in modeling with a four level system the near resonant cubic susceptibility of the polydiacetylene, poly(4-BCMU). In that case tunable Third-Harmonic-Generation and Two-Photon-Absorption measurements both agreed with the result of a Near-Infrared-Three-Wave-Mixing measurement. In the case of β-carotene and polythiophenes the four level model also fits the Third-Harmonic-Generation data well. In the previously mentioned cases the spectral behavior of the Two-Photon figure of merit derived by Mizrahi et al. is calculated. The four level model, when extrapolated far off resonance predicts that an all-optical switching device constructed with these materials will be dominated by Two-Photon-Absorption. A promising new class of side-chain substituted polymers with large microscopic second order nonlinearities was also investigated. Third-Harmonic-Generation measurements indicate that no forbidden two-photon transition is present in this case and that the magnitude of the nonlinear third order susceptibility is dominated by the charge-transfer nature of the nonlinear moieties combined with cascading of second order effects at a microscopic level. In the case of Sol-Gel thin films of varying TiO₂ concentration in SiO₂, the formula derived by Boling et al., based also on a three level model, predicts successfully the magnitude of the third order susceptibility. THG is in that case an invaluable technique used for the first time to measure relatively small nonlinear susceptibilities of glass-like thin films.

This dissertation presents results on the study of the temperature and internal state dependence of ion-neutral reactions. The free jet flow technique is used to measure rate coefficients for several reactions at ultralow collision energies near 1 K. The technique, and the unique considerations of free jet flow are considered. The method of analysis of the data obtained from the free jet reactor is also presented. The measurement of reaction rate coefficients for several fast reactions is reported. These studies demonstrate the utility of the technique as various types of reactions which occur at the collision rate are studied. Reactions which do not occur at the collision rate have also been studied. Several slow reaction rate coefficients of the atomic ion AR⁺ are measured, and the data acquired from the free jet flow reactor aids in the elucidation of the reaction mechanisms for these systems. The slow reaction between C₂H₂⁺ and H₂ is also considered, and a theory to account for its unusual temperature dependence is presented which depends heavily on the formation of a long lived collision complex. The experimental rate coefficients for three body association reactions of the rare gas atomic ions Ar⁺, Kr⁺ and Xe⁺ are presented. The experimental results in this case show very large rate coefficients which cannot be explained satisfactorily by any current theories. Using resonantly enhanced multiphoton ionization to create quantum state specific ions, the measurement of rate coefficients for selected vibrational states of molecular ions and spin orbit states of atomic ions are reported. Observed effects for vibrational excitation of molecular ions and spin-orbit excitation of atomic ions are discussed. Finally, the production and subsequent dynamics of negative ions by electron attachment are examined. The electrons are produced from a high resolution source by using two color resonantly enhanced multiphoton ionization spectroscopy on a suitable precursor.

The coupled-cluster (CC) equations including single, double, triple and quadruple excitations (CCSDTQ) are qraphically derived using Feynman diagrams. These equations are programmed and an iterative reduced linear equation method is used to solve these equations. A few points on the potential curves for the dissociation of some model systems with a single bond (LiH and Li₂) are calculated using CC doubles (CCD), singles and doubles (CCSD), singles, doubles and triples (CCSDT) and CCSDTQ. These calculations demonstrate the magnitude of the CC contributions arising from triple and quadruple excitation amplitudes to the stretching of a chemical bond. A multi-reference coupled-cluster singles and doubles (MRCCSD) method utilizing two reference determinants, which differ by a two electron excitation, is then proposed. One of these determinants is selected as the formal reference determinant. The proposed method is based on the single-reference coupled-cluster equations truncated after quadruples with appropriate restrictions placed on the triple and quadruple amplitudes to allow only those amplitudes which correspond to single and double excitations from the second reference determinant. The computational expense of this method is no more than twice that of singles and doubles from a single reference (CCSD). These equations are programmed and the potential curves for the dissociation of a few model systems with single bonds (LiH, BH, and H₂O) are calculated to demonstrate the correct bond dissociation properties of this method. These calculations also demonstrate how much of the CC energy contribution arising from the triple and quadruple excitation amplitudes can be attributed to single and double excitations from the second reference determinant.