Doctor of Philosophy, University of Akron, 2007, Polymer Science

One of the biggest challenges in solid state physics today is understanding the nature of the glass transition. Dynamic studies are critical in solving some of the problems in the field. Until recently, investigations of dynamics in glass formers were mostly carried out as a function of temperature. However, with the advancements in experimental techniques and methods, the interest towards using pressure as an additional experimental variable increased. The advantages of pressure over temperature are two-fold: First, it only alters the density of the system, whereas temperature changes both the thermal energy and the density, and secondly, one can achieve significant density changes (~20%) with pressure, whereas temperature creates smaller density changes (~5%). These advantages let researchers make direct comparisons of the results with glass transition models (i.e. free volume ideas). The dynamics in the frequency range between 1 GHz and 5 THz (fast dynamics), are thought to have a crucial role. Crystals in this frequency range have a Debye-like density of vibrational states. Glasses, however, have two extra contributions when compared to crystalline structures: (i) an anharmonic relaxation-like contribution that appears as a quasielastic scattering (QES) and (ii) a harmonic vibrational contribution, which shows up as the boson peak (BP) in light and neutron scattering spectra. It has also been shown experimentally that fast dynamics in glasses are strongly correlated with the temperature dependence of structural relaxation.In this dissertation the influence of pressure on fast dynamics in polyisobutylene, polyisoprene and low molecular weight polystyrene is investigated using inelastic light, neutron and X-ray scattering techniques. The results are compared to the predictions of the existing models.The results for all polymers studied showed that the boson peak shifts more strongly than sound modes, suggesting that the variations cannot be fully described by the (open full item for complete abstract)

Committee: Alexei Sokolov (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2015, Geological Sciences

The structure, dynamics, and composition of Earth's deep interior have direct control on plate tectonics and surface-to-interior exchange of material, including water and carbon. To properly interpret geophysical data of the Earth's interior, accurate and precise measurements of the material properties of the constituent mineral phases are required. Additionally, experimentally derived data need to be augmented by computational chemistry and modeling of physical properties to elucidate the effect of compositional variations and deep storage of volatile components (e.g. H2O and CO2) within the crystalline phases. This dissertation uses in situ high pressure, high-temperature experiments in the laser-heated diamond anvil cell (LHDAC) coupled with synchrotron-based x-ray diffraction. The thermal expansion and bulk modulus of Ni and SiO2 are measured to P = ~110 GPa and T = ~3000 K. Nickel is a significant component of the Earth's core and SiO2 is the fundamental building block of the Earth's mantle and crust. We have designed the first controlled-geometry samples of Ni and SiO2, manufactured using nanofabrication techniques, and specifically tuned to reduce systematic errors in the measurement. Knowledge of the thermoelastic properties of Ni and SiO2 has implications for subduction rates, plume buoyancy, dynamics of the Earth's convective heat engine, and planetary formation. Complimentary to the Ni/SiO2 experiments, the energetics of different hydrogen defect mechanisms in garnet (MgSiO3-Mg3Al2Si3O12) and associated geophysical properties (P- and S-wave velocities) are calculated using atomistic simulations and first-principles calculations to a depth of 700 km. Garnet accounts for as much as 40 percent of the rock volume at 500 km. By calculating and comparing the defect energies associated with charge-balanced substitutions of hydrogen for magnesium or silicon, the hydrogarnet defect has the lowest energy and is therefore predicted to be the most favorable in the ga (open full item for complete abstract)

Committee: Wendy Panero (Advisor); Berry Lyons (Committee Member); Michael Barton (Committee Member); David Cole (Committee Member) Subjects: Earth; Geological

Master of Science, The Ohio State University, 2011, Geological Sciences

The viscosity of water is a first-order constraint on the transport of material from a subducting plate to the mantle wedge. The viscosity of fluids that are released during the dehydration of hydrous minerals during subduction can vary by more than 9 orders of magnitude between the limits of pure liquid water and silicate melts. Accurate determination of low viscosities (<1 mPa·s) for liquids at simultaneous high pressures (>1 GPa) and high temperatures (>373 K) is hindered by the geometry and sample size of high-pressure devices. Here the viscosity of water at pressures representative of the deep crust and upper mantle through use of Brownian motion in the hydrothermal diamond anvil cell (HDAC) is reported. By tracking the Brownian motion of 2.8 and 3.1 micron polystyrene spheres suspended in H2O, the viscosity of the water at high pressure and high temperature can be determined in situ using Einstein's relation. Accuracies of 3-10% are achieved and measurements are extended to pressures relevant to fluid release from subducting slabs and temperatures up to 150% of the melting temperature. Unhampered by wall effects of previous methods, the results from this study are consistent with a homologous temperature dependence of water viscosity in which the viscosity is a function of the ratio of the temperature to the melting temperature at a given pressure. Based on the homologous temperature dependence of water, transport times for fluids released from subducted plates inferred from geochemical proxies are too short for transport via porous flow alone, and suggest transport through a combination of channel-flow and porous flow implying hydrofracturing at 50-150 km depth.

Committee: Wendy Panero (Advisor); Michael Barton (Committee Member); David Cole (Committee Member) Subjects: Geophysics