Doctor of Philosophy, The Ohio State University, 2007, Pharmacy

Supercritical fluid technology, specifically the method of rapid expansion of supercritical solutions (RESS), has been used to prepare small particles consisting of solid solutions of a relatively insoluble drug and a water-soluble excipient. With an increasing number of relatively insoluble compounds being discovered, a general process for enhancing drug dissolution rates would assist formulation of these compounds for therapeutic use. Solid solutions could serve as a means for enhancing drug dissolution rates, since the drug is dispersed in a solid solvent in its smallest form, i.e., a molecule, prior to entering into solution. Therefore, solid solutions consisting of the relatively insoluble model drugs lidocaine or probucol and a water-soluble surfactant, poloxamers 407, 188, or 403 were prepared by RESS processing. Dissolution studies of these systems were performed and evaluated for their ability to enhance drug release rates. Furthermore, the mechanism by which solid solutions form in these systems was determined using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) was also used to study the surface characteristics of these particulate systems. Dissolution studies of these particles showed an enhanced rate of release of drug in the presence of poloxamer. This enhancement was due to the apparent formation of solid solutions. DSC of these particulate systems also indicated the formation of solid solutions of drug and poloxamer with increasing proportion of poloxamer. With the formation of solid solutions, hydrogen bonding occurred between the drug and poloxamer. This bonding was dependent on the polyoxyethylene chain length of the three poloxamers, i.e., where hydrogen bonding primarily occurs. Solid solutions formed for systems consisting of drug and poloxamers 407 or 188, which have similar polyoxyethylene lengths and hence similar amounts of available sites for bonding. Solid sol (open full item for complete abstract)

Committee: Sylvan Frank (Advisor) Subjects:

Master of Science, The Ohio State University, 1962, Graduate School

Committee: Not Provided (Other) Subjects:

Doctor of Philosophy, University of Toledo, 2021, Physics

This dissertation is a systematic computational investigation of transition metal nitrides in M4N structure and in two alloy systems of Ti1-xScxN and Ti1-xYxN (0 ≤ x ≤ 1). Transition metal nitrides constitute a class of materials which have been broadly applied in the industry of hard coatings and cuttings. Our objective is to expand the currently existing database of these materials by exploring their structural, mechanical, magnetic, electronic, and thermodynamic properties, stability and hardness using the state-of-the-art first principles computational approach. Chapters 4 and 6 contain the main results and are summarized as follows. 1. We performed first-principles calculations with density functional theory on 28 metal rich cubic binary M4N structures. We provided a high through-put database of mechanical, electronic, magnetic, and structural properties for these compounds. We observed three compounds with Vickers hardness around or above 20 GPa, such as Re4N, Tc4N, and Mn4N (Chapter 4). We also identified 25 M4N compounds as mechanically stable while the remaining 3 (V4N, Nb4N, and Pt4N) as unstable. 2. We showed the relationship between the hardness and stability of these compounds and the density of states. We also calculated the magnetic properties of five magnetic compounds and exhibited that the consideration of electronic spin-polarization is very important in accurately calculating ground state energy and hence mechanical properties of these transition metal nitrides. 3. We also studied the phase stability, mechanical and electronic properties of two ceramic quasi-binary systems, Ti1-xScxN and Ti1-xYxN using density functional theory, cluster expansions and Monte Carlo simulations. We predicted strong exothermic mixing of TiN and ScN due to cationic similarity with the formation of 4 novel intermetallic compounds TiScN2, TiSc8N9, TiSc9N10, and Ti3Sc2N5 in the Ti1-xScxN system having hardness as high as 27.3 GPa. The phase diagram of Ti1-xScxN sys (open full item for complete abstract)

Committee: Sanjay Khare Dr. (Committee Chair); Jacques Amar Dr. (Committee Member); Richard Irving Dr. (Committee Member); Aniruddha Ray Dr. (Committee Member); Anju Gupta Dr. (Committee Member) Subjects: Physics

Doctor of Philosophy, University of Toledo, 2017, Physics

This dissertation is a computational exploration of transition metal nitrides, a group of materials that have myriad applications in the hard coatings industry. We aim to explore their structural, mechanical, electronic and thermodynamic properties and their solid solutions, discovering trends and correlations of their bonding nature and cause of superior stability and hardness. Here are the major work and results: 1. We performed first-principles calculations with density functional theory on six cubic structural prototypes, zincblende, rocksalt, cesium-chloride, NbO, fluorite and pyrite. We observed a few compounds with Vickers hardness higher than 20 GPa, such as rocksalt-structure ScN, TiN, cesium-chloride-structure VN, NbO-structure CrN, MoN, WN, and pyrite-structure MnN2, PtN2. (Chapter 4, Chapter 5 and Chapter 6) 2. We established an anti-correlation between metallic compounds' total electronic density of states at the Fermi energy level, an indicator of metallicity and their shear-related mechanical properties, such as elastic constant C44, shear modulus, Pugh's ratio and Vickers hardness. (Chapter 4, Chapter 5 and Chapter 6) 3. Beyond single-cation phases, we further studied the phase equilibria of three ceramic quasibinary systems, Ti1-xZrxN, Ti1-xHfxN and Zr1-xHfxN. We analyzed the asymmetry of composition-dependent formation energy curves through two energetically partially canceling processes. We concluded that the absence of experimental observations of phase separation, as predicted by our calculations in Ti1-xZrxN and Ti1-xHfxN is probably due to a combined effect of insufficient undercooling, inadequate atomic diffusivity, and the initial energy barrier for chemical exchange with constrained lattices. (Chapter 8) 4. We also showed that mixing nitrides of same group transition metals does not lead to hardness increase from an electronic origin, but through solution hardening mechanism, a plastic phenomenon difficult to catch with first-pr (open full item for complete abstract)

Committee: Sanjay Khare (Committee Chair); Jacques Amar (Committee Member); Nikolas Podraza (Committee Member); Bo Gao (Committee Member); Daniel Georgiev (Committee Member) Subjects: Physics