Owing to the favored Coulombic attraction between the ammonium group and anion which stabilizes the B-F/B-CN bond against heterolysis, cationic borane [25]+ has great affinity toward anions than its neutral analog, and is capable of capturing fluoride or cyanide from water under bi-phasic conditions. By placing the fluorophilic silyl group adjacent to an electrophilic carbocation, a novel fluoride sensor [45]+ was obtained. Sensing occurs via a fluoride induced methyl migration from the silicon to adjacent electrophilic methylium center which is unprecedented. As a result of its strong fluoride affinity, [45]+ is able to react with KF in aqueous media at pH 7.0. The electrochemistry study of these cationic Lewis boranes reveals that the cationic character of these boranes serves to decrease their reduction potential and increase the stability of the resulting radicals. In this part of the research, we have prepared a cationic borane [27]+, which features two reversible reduction waves at -0.86 and -1.56 (vs. Fc/Fc+) corresponding to the formation of stable neutral and anionic derivatives. The one-electron reduction of [27]+ leads to the formation of a boron containing neutral radical featuring an unusual boron-carbon one-electron π bond. Further reduction of 27• results in the formation of the borataalkene derivative [27]-, which features a formal B=C double bond. The structural changes accompanying the stepwise population of the B-C π-bond are also determined, and this sequential population of B-C π-bonding orbital is also supported by theoretical computations. In order to understand the impact of the cationic nature of these boranes on their oxidative power, three novel cationic boranes ([34]+, [35]2+, and [36]3+) have been synthesized and their oxidative power were examined via cyclic voltammetry. The CV data of these compounds shows that the reduction potential of these triarylboranes is linearly proportional to the number of the pendant cationic substituents. Substitution of a mesityl group by an ArN+ group leads to an increase of the reduction potential by 260 mV.

The aim of this study was to investigate the microstructure, microhardness and biocompatibility properties of nano hydroxyapatite (HA) doped with a constant yttrium (Y3+) and varying fluoride (F-) compositions. HA was synthesized via precipitation method and sintered at 1100&amp / #61616 / C for 1 hour. Increased densities were achieved upon Y3+ doping while F- doping led to a decrease in densities. For structural analysis, XRD, SEM and FTIR spectroscopy examinations were performed. No secondary phases were observed in XRD studies upon doping. Lattice parameters decreased due to substitutions of ions. In SEM analysis, addition of doping ions was observed to result in smaller grains. In FTIR analysis, in addition to the characteristic bands of HA, novel bands indicating the substitution of F- ions were observed in F- ion doped samples. The highest microhardness value was obtained for the sample doped with 2.5%Y3+, 1%F-. Increased F- ion contents resulted in decreased microhardness values. For biocompatibility evaluation, in vitro tests were applied to the materials. MTT assay was performed for Saos-2 cell proliferation analysis. Y3+ and F- ion incorporation was found to improve cell proliferation on HA discs. Cells were found to attach and proliferate on disc surfaces in SEM analysis. ALP assay showed differentiation of cells on the discs can be improved by doping HA with an optimum amount of F- ion. Dissolution tests in DMEM revealed that structural stability of HA was improved with F- ion incorporation. The material exhibiting optimum structural, mechanical and biocompatibility properties was HA doped with 2.5%Y3+, 1%F-.

The purpose of this study was to synthesize calcium phosphates doped with titanium and fluoride ions in different combinations. Pure and doped calcium phosphates were synthesized by a precipitation method. The synthesized materials were sintered at 1100&ordm / C and 1300&ordm / C for 1h. The ceramics were characterized by density measurements to determine the effect of sintering temperature. Presence of phases and bonds were characterized by XRD diffraction and FTIR spectroscopy. Grain sizes of the samples were obtained by SEM. Microhardness test was applied on the samples to determine the mechanical properties of the samples. It was observed that Ti4+ addition decreased the density of samples significantly at 1100&deg / C, whereas increasing the sintering temperature to 1300&deg / C caused an increase. Increasing the F- ion amount increased the densification at 1100&deg / C when molar ratios were 1.0, 1.25, 1.50 and decreased the density at 1300&deg / C when Ca /P molar ratios were 1.0, 1.25, 1.67 and 2.0. Ti4+ and F- co-doped samples showed variety in their density behaviour after the sintering at 1100&ordm / C and 1300&ordm / C. The XRD analyses demonstrated that for Ca to P ratio 1 at 1100&deg / C, &beta / -CPP phase, when sintering temperature was raised to 1300&deg / C, as a second phase of &beta / -CPP and &alpha / -TCP observed. Increasing the molar ratio to 1.25 and 1.50 demonstrated &beta / -TCP and/or &beta / -CPP and &beta / -TCP/ HA at 1100&deg / C and &beta / -TCP and/or &beta / -CPP, &alpha / -TCP, TiO2 and HA, &alpha / -TCP, TiO2 phases at 1300&deg / C, respectively. In higher Ca/P molar ratios of 1.67 and 2.0, HA, &beta / -TCP, &alpha / -TCP, CaO, TiO2, CaTiO3 and HA, CaO, &alpha / -TCP, CaTiO3 phases were determined. Increasing the sintering temperature to 1300&deg / C resulted in transformation to &alpha / -TCP. In FTIR spectroscopy analysis, when the samples with molar ratio of 1, 1.25, 1.50, 1.67 and 2.0, sintered at 1100&deg / C, the characteristic bands of &beta / -CPP, OCP/&beta / -TCP, &beta / -TCP/HA, HA and HA were observed, respectively. With increasing the sintering temperature to 1300&deg / C, samples with molar ratio of 1.0 and 1.25 revealed additional secondary characteristic peaks of HA and &beta / -TCP. SEM images revealed that sintering temperature and ion amounts of dopants had significant effect on grain sizes of the samples. The grain sizes were generally increased when sintering temperature rose from 1100&deg / C to 1300&deg / C. The &mu / -hardness test demonstrated that Ti4+ and F- ions in large amounts had positive effect on the mechanical properties at the sintering temperatures of 1100&deg / C and 1300&deg / C

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 97-104).

The applications of membrane technologies have dramatically increased during the last few decades due to technology improvement and cost reduction. Membrane applications can be found in water and wastewater treatment, pharmaceutical industry, chemical processing industry, food industry, etc. However, the membrane technology faces two major challenges: membrane fouling and membrane lifetime. During the membrane filtration process, membrane fouling caused by natural organic matter (NOM) is an inevitable phenomenon, and physical cleaning or chemical cleaning are required for recovering the performance of membrane. As a result of these cleaning processes, membrane lifetime is shortened. For this reason, it is necessary to improve membrane's fouling resistance and lifetime in order to apply membrane technology in large-scale facilities. This dissertation focuses on improving the fouling resistance and flux performance of polyvinyl chloride (PVC) membrane and polyvinylidene fluoride (PVDF) membrane. Specifically, it is comprised of four parts. First, I prepared PVC membranes by adding different amounts of amphiphilic copolymer (Pluronic F 127) into PVC casting solutions. I optimized the performance of PVC membranes by changing the amount of Pluronic F127 used in the casting solution. The results show that with the increase of Pluronic F 127 content, the pore size and pore density both decrease. Moreover, the membrane surface becomes more hydrophilic as indicated by lower contact angles. In addition, the PVC membrane exhibits remarkable antifouling characteristics after adding Pluronic F 127. Second, I synthesized PVDF membranes by adding PVDF graft poly(ethylene glycol) methyl ether methacrylate (PEGMA) (PVDF-g-PEGMA) as additive in casting solutions via the phase inversion method. The synthesized PVDF membranes have unique pillar-like structures on surfaces, which gives the PVDF membrane a defect-free feature and allows it to generate high flux under low pressure. Third, I investigated the forming mechanism of the pillar-like structure from aspects of solvent and additive. Finally, I investigated the influence of PEGMA dose on the performance of PVDF membranes. I changed the amount of PEGMA used in the casting solution and compared the performance of the synthesized PVDF membranes. To summarize, this dissertation has deepened our understanding of how to improve the fouling resistance and flux performance of PVC membranes and PVDF membranes by using amphiphilic copolymer. In addition, the PVDF membrane I synthesized has unique pillar-like structures that give it defect-free and high flux properties. Overall, the results of this study provide valuable information for PVC and PVDF membrane synthesis for large-scale production.

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

No description available.

No description available.

Consistent evidence confirms that the addition of fluoride to achieve an optimal concentration in potable water supplies is both safe and effective in reducing community caries experience. While public acceptance and use of water fluoridation in Australia has been high for forty years, its implementation in Queensland remained low until December 2008. Political and social scientists have long recognised that the formation and maintenance of public policy in Australia is a complex interactive process involving inter alia government, bureaucracy, pressure groups and voters. However, explanations of the factors influencing the outcome of a proposal to fluoridate a municipal water supply remain inadequate. The long evolution of adjusted fluoridation has its genesis in pre-1930 North American concerns over the disfigurement associated with endemic dental mottling. Throughout the 1930s and 1940s, many perceived this affliction as the visible manifestation of a public health problem: chronic fluoride intoxication. Reports of environmental contamination of the food chain from naturally over-fluoridated water and agrarian and industrial practices only increased community doubts about the accumulative and toxic potential of fluoride. For these and other reasons the public perception of fluoride was poor. Between 1937 and 1945, USPHS dental researcher and later Director of the National Institute of Dental Research HT Dean and co-workers emerged as the few who understood the fine line between fluoride therapy and toxicity. Their investigations involved not only specialised interpretations of human dental epidemiology but also multidisciplinary studies of human and animal fluoride exposure and homeostasis. However, decisions to implement water fluoridation had to come from the relevant government authorities. Here scientific knowledge faced political reality. Apart from perceived safety issues and resistance to the compulsory nature of water fluoridation, many other barriers to water fluoridation emerged: incompletely understood pharmacodynamics of fluoride; confounding issues in the initiation and propagation of caries; community acceptance of this epidemic; and political sensitivities regarding water. This scientific and social background explained why adjusted fluoridation was amenable to both challenge and misrepresentation. In the US, the constitutional, institutional and financial network provided the basis for an enduring culture of dental research that eventually provided the multidisciplinary evidence to endorse the safety and efficacy of water fluoridation. Although Australians did not experience a widespread human mottling problem akin to that in the United States, Australian fluoride advocates faced similar opposition. The Australian constitution, state parochialism and decentralisation compounded by vast distances fragmented the responsibilities for research, health and water treatment. Each state had limited resources and faced these responsibilities in its own way. Although there were several early attempts in some states at regional dental field studies, meaningful national dental epidemiology did not emerge until 1993. Hence, much of the supportive evidence for fluoridation in Australia had to be imported from North America. This background meant that wherever fluoridation was widely implemented in Australia, state authority played a role. In addition to the general social and scientific concerns about fluoride and fluoridation, before 1957 there were a number of unresolved scientific factors relating to naturally over-fluoridated ground water, climate, tea consumption and fluid homeostasis involving canecutters. These made Queensland different in the Australian context. After 1957, as these scientific concerns in Queensland diminished, the political landscape changed and provided new foundations for political hesitance and expedience. The timing and circumstances of the promulgation of the Fluoridation of Public Water Supplies Act (1963) influenced its nature to the extent that until 2008, this legislation with its link to various local government acts was unique within Australia. Although there were notable exceptions such as the decisions to fluoridate water supplies at Townsville and Mareeba, this legislative background established the “Queensland difference” as a fixture in fluoride debates across the state. When combined with inadequate state funding and a lack of political resolve from parliamentarians and councillors, prospects for fluoridation in Queensland were virtually paralysed. Nonetheless, while inquiry into the political reasons for the implementing or the failure to implement fluoridation remains thin, developments in Queensland after December 2007 lend significant weight to the finding that a politically resolute centralised authority with the responsibility for both health and water are key components in the outcome.

Universiẗat, Diss., 2003--Münster (Westfalen).