A solar simulator was used to test whether a carbon black additive could increase the solar absorption of a low temperature organic PCM (consisting of a eutectic mixture of palmitic acid and stearic acid). Various PCM and carbon black composites (0.01 % to 6 %) were tested, with the 0.06 % carbon black composites showing the fastest temperature increase, reaching 75 °C much quicker (350 % faster) than the pure PCM. All of the tested PCM composites reached 75 °C in less than half the time it took the pure PCM. It can therefore be seen that carbon black is very effective at increasing the solar absorption of the PCM. The carbon black did not have a negative impact on the melting/solidifying onset temperature or the latent heat of the PCM. This proves that at these low concentrations carbon black can help reduce the shortcomings of the PCM without adversely affecting its energy storage properties. The optimal carbon black concentration changes with the size of the PCM: a shallow PCM layer (2 cm) showed the fastest temperature increase at higher concentrations (between 0.06 % and 0.5 % carbon black), while the deep PCM layer (9 cm) showed the fastest temperature increase at lower concentrations (between 0.01 % and 0.08 % carbon black). The poor optical properties of the PCM were vastly improved by the carbon black, making the composite an effective direct solar absorber. The carbon black, however, does not provide meaningful thermal conductivity enhancements. Therefore additional heat transfer enhancements (like graphite) are needed if this novel PCM composite is to be used in a combined system (direct solar absorber, heat transfer fluid and energy storage system). / Dissertation (MEng)--University of Pretoria, 2016. / Chemical Engineering / MEng / Unrestricted

Urea forms crystalline complexes with n-alkanes and their liner derivatives but not with most branched and cyclic hydrocarbons and their derivatives. The compounds are stable enough to be used in separating these types of aliphatic compounds from their branched and cyclic analogs. Linear esters derived from normal saturated acids give adducts as expected. Urea complexation was found to be of great importance in the purification and separation of unsaturated esters of high molecular weight. The object of the present research was to investigate the compositions of urea adducts of various long-chain esters, approaching the class of waxes, to test various methods of determining their compositions, and to determine the suitability of the adduct method for purifying such esters.

Dietary saturated fat intake contributes to diabetes and cardiovascular disease, as shown in numerous animal and human studies. However, the hypothesis that stearic acid, a saturated fat, has beneficial effects on these conditions has not been adequately tested. Leptin receptor deficient mice (db/db) and wild-type mice were fed either chow or a high fat diet enriched in either stearic acid or oleic acid for ten weeks. The progression of diabetes was evaluated with blood glucose, insulin, and metabolic parameter measurements. At the conclusion of the study, pancreatic islet organization was examined, and blood, liver and feces were assayed for fatty acid content. The stearic acid enriched diet prevented increases in blood glucose levels independently of weight loss in db/db mice compared to an oleic acid or chow diet. Diabetic mice fed stearic acid maintained insulin responsiveness and pancreatic islet organization compared to the db/db mice fed chow and oleic diets. The islet organization of the stearic acid fed mice did not change over the course of the study and was similar to that of wild-type mice fed the same diet. Conversely, diabetic mice fed oleic acid and chow diets had decreased insulin responsiveness and disorganized islets. Stearic acid fed db/db mice had high fecal fat content and caloric intake calculations indicated low absorption of this fat. Switching to stearic acid after prolonged hyperglycemia had a rescue effect on blood glucose levels. After feeding diabetic and wild-type mice standard chow diets for 6, 8, and 10 weeks to establish hyperglycemia, mice switched to a high fat diet enriched in stearic acid, but not one enriched in oleic acid diet, had significant reductions in blood glucose levels. The ability of a stearic acid enriched high fat diet to slow the progression of diabetes and reverse hyperglycemia in db/db mice argues that risks and benefits of fats in the diet depend on the chemical structure, rather than the chemical class, of fats ingested. The beneficial effect of stearic acid appears to be associated with a decreased absorption of dietary fat.

A aterosclerose é classificada como enfermidade crônica não transmissível e é considerada uma das principais causas de morte e morbidade em vários países, incluindo o Brasil. Entre as possíveis causas de sua gênese está o hábito alimentar, especificamente o consumo de ácidos graxos, principalmente saturados e trans. Ácidos graxos saturados possuem características biológicas e fisico-químicas diferentes dos insaturados. Os mais abundantes na dieta humana são o palmítico e esteárico. Sua associação com acometimentos cardiovasculares vem sendo cada vez mais investigada, principalmente os que possuem mais de dez carbonos em sua cadeia interferindo no metabolismo de lipoproteínas podendo desencadear todo o processo aterosclerótico. A indústria de alimentos vem desenvolvendo algumas tecnologias opcionais para reduzir ou eliminar ácidos graxos trans, em especial, o elaídico, dentre elas a modificação no processo de hidrogenação que aumenta a quantidade de ácidos graxos saturados. Alguns alimentos industrializados necessitam de uma grande quantidade de ácidos graxos saturados promovendo um aumento no teor de ácido palmítico e esteárico, sendo este último considerado um ácido graxo saturado neutro, mas dependendo da concentração utilizada, pode contribuir no decréscimo da HDL-c (High Density Lipoprotein), dentre outras alterações deletérias. Desta forma, investigar as alterações de determinados parâmetros biológicos diante da mudança da proporção de ácidos graxos saturados, respeitando o teor total de lipídios de uma dieta é a base deste estudo. Foram realizados ensaios em material biológico para a determinação dos seguintes parâmetros: 1) Atividade de enzimas antioxidantes; 2) Peroxidação lipídica em tecidos; 3) Lipidograma; 4) Determinação do perfil de ácidos graxos de tecidos e rações e 5) Expressão de genes relacionados com o processo aterosclerótico (ICAM-1, VCAM-1, CD36 e MCP-1). A determinação da atividade de enzimas antioxidantes foi realizada considerando somente as enzimas Catalase (CAT) e Superóxido Dismutase (SOD), por se tratarem de enzimas com alteração expressiva no processo aterogênico, na ocorrência de disfunção endotelial. Neste trabalho, foi analisada a atividade das referidas enzimas no tecido hepático e cardíaco, onde não foram constatadas alterações. O mesmo processo biológico que estimula a produção excessiva de espécies reativas pode levar ao aumento da peroxidação lipídica, principalmente de ácidos graxos polinsaturados das membranas celulares, em tecidos como fígado, cérebro e coração. A peroxidação lipídica apresentou diferenças significativas no tecido hepático. O grupo alimentado com ração enriquecida com tripalmitato apresentou peroxidação lipídica aumentada em relação ao grupo controle. Correlacionando com o perfil de ácidos graxos do tecido hepático, notamos que houve maior incorporação de ácido palmítico nesse tecido, que por apresentar configuração linear, quando incorporado à membrana celular, pode levar à disfunção e possível suscetibilidade a danos, como a peroxidação. No tecido cardíaco e no tecido cerebral não foram observadas alterações e diferenças entre os tratamentos. O lipidograma consiste na quantificação de lipoproteínas e frações lipídicas, compondo o perfil lipídico no plasma sanguíneo. Os resultados obtidos mostraram que o colesterol total foi significativamente menor no grupo controle, assim como triacilglicerol e LDL colesterol (LDL-c). Já HDL colesterol (HDL-c) está reduzida no grupo que recebeu ração suplementada com ácido palmítico, assim como este grupo apresentou parâmetros aumentados nas dosagens de triacilglicerol e colesterol total. Os grupos alimentados com ração suplementada com triestearato e trioleato apresentaram resultados intermediários para a dosagem de HDL-c, com valores tendendo ao grupo suplementado com tripalmitato. Em relação à dosagem de LDL-c, foi constatada diferença entre os grupos suplementados e o grupo controle. Destaca-se que não houve diferença entre a dosagem entre os grupos suplementados. Portanto, o grupo alimentado com dieta enriquecida com ácido oleico (monoinsaturado) equipara-se aos grupos alimentados com dietas enriquecidas com ácido esteárico e palmítico (saturados). O perfil de ácidos graxos do tecido hepático mostrou uma porcentagem elevada de ácido palmítico no grupo alimentado com ração enriquecida com o mesmo ácido graxo, com diferença estatística em relação aos demais grupos. Já em relação ao ácido esteárico, não houve diferenças significativas entre os grupos. Em compensação, o teor de ácido oleico no grupo suplementado com este mesmo ácido graxo e com ácido palmítico foi significativamente diferente em relação aos demais, com valores superiores. Este resultado demonstra que não houve dessaturação do ácido esteárico a oleico, ao menos neste modelo. No tecido cardíaco, foi observado o mesmo comportamento. No tecido cardíaco não houve diferença estatística significativa da concentração de ácidos graxos, indicando que não houve incorporação ou dessaturação. Ressalta-se que de acordo com determinação realizada utilizando a técnica de cromatografia gasosa, as rações apresentavam em sua composição o teor de lipídios adequado ao modelo animal e as proporções de ácidos graxos alteradas como proposto no objetivo deste trabalho. Em relação às moléculas de adesão e quimiocinas (VCAM-1, ICAM-1, CD-36 e MCP-1) relacionadas com o processo aterosclerótico, houve somente alteração na molécula CD-36 no grupo alimentado com ração enriquecida com trioleato, com redução em relação aos demais. Mas, as moléculas de adesão relacionadas com o processo inicial da aterogênese, a expressão gênica realizada através da técnica de q-RT-PCR não foi relevante, não apresentando diferença entre os tratamentos. Conclui-se, portanto, que os tratamentos aplicados ao modelo animal selecionado possui o potencial de alterar lipoproteínas plasmáticas, mas não de manter a continuidade e desencadear o processo inflamatório relacionado à aterogênese. / Atherosclerosis is chronic a non-communicable disease considered one of a major cause of morbidity and mortality in several countries, including Brazil. Among all the possible causes of their genesis the dietary habit of high fatty acid intake, especially saturated and trans fatty acids is the most important. Saturated and unsaturated fatty acids possess different biological and physicochemical characteristics. The most abundant fatty acid in the human diet are palmitic and stearic and they association with cardiovascular events has been increasingly investigated, especially those one with more than ten carbons in its chain which interfers in the lipoproteins metabolism and can initiate the atherosclerotic process. The food industry has developed some optional technologies to reduce or eliminate the presence of trans fatty acids in foods, in particular elaidic, which after the hydrogenation process increases the saturated fatty acids content. Some industrialized foods requires a large amount of saturated fatty acids that promote an increase of palmitic and stearic content, the last fatty acid mentioned is considered a neutral saturated fatty acid that can contribute to the decrease in HDL-c (High Density lipoprotein), depending on the concentration used, among other deleterious changes. Thus, investigate changes of specifics biological parameters in response to consumption of different saturated fatty acids, respecting the total content of lipids in a normolipidic diet is the aim of this study. Assays were conducted to determine the following parameters in the tissues: 1) Activity of antioxidant enzymes, 2) Lipid peroxidation, 3) Lipidogram; 4) Fatty acid composition 5) Expression of genes related the atherosclerotic process (ICAM-1, VCAM-1, CD36 and MCP- 1). The determination of the activity of antioxidant enzymes was carried out considering only the enzymes Catalase (CAT) and Superoxide Dismutase (SOD), because they are enzymes more sensitive and readily available in changes resulted of an atherosclerotic process with endothelial dysfunction. In the study, no changes were observed in activity of these enzymes in the liver and heart. The same biological process that stimulates the overproduction of reactive species can lead to increased lipid peroxidation, especially of polyunsaturated fatty acids present in cell membranes of tissues such as liver, brain and heart. The group fed with diet enriched with tripalmitate showed increased lipid peroxidation compared to control group. Correlating this information with the fatty acid profile in liver tissue, we noted that there was a greater incorporation of palmitic acid, which exhibit linear configuration when incorporated into the cell membrane and can lead to dysfunction and higher susceptibility to damages such as oxidation. No differences were observed in the others tissues analyzed. The lipidogram is the quantification of lipoprotein and lipid fractions, composing the lipid profile in blood plasma. The results showed that total cholesterol was significantly lower in the control group, as well triglyceride and LDL cholesterol (LDL-c). HDL cholesterol (HDL-C) concentration is reduced and triacylglycerol and cholesterol increased n the group fed with diet supplemented with palmitic. The groups fed with diets supplemented with tristearate and trioleate presented intermediate results for the measurement of HDL-c, with values tending to the group supplemented with tripalmitate. Regarding LDL-c levels, significant differences were observed between the supplemented groups and the control group. Emphasis that there was no difference between the dosage between the supplemented groups. Therefore, the group fed with oleic acid (monounsaturated) supplemented diet equates to the groups fed with diets enriched with stearic and palmitic acid (saturated). The fatty acid profile of liver tissue showed a high percentage of palmitic acid in the group fed with diet enriched with the same fatty acid, with a statistical difference compared to the other groups. In relation to stearic acid, there were no significant differences between groups. As compensation, the oleic acid content in the group supplemented with the same fatty acid and palmitic acid was significantly higher when compared to the others. This result demonstrates that no desaturation of stearic acid to oleic happened in this experimental model. In cardiac tissue there was no statistically significant difference in the concentration of fatty acids, indicating no incorporation or desaturation. Regarding adhesion molecules and chemokines (VCAM-1, ICAM- 1, CD-36 and MCP-1) related to the atherosclerotic process, there was only change in the gene expression of CD-36 molecule in the group fed diet enriched with trioleate, with reduction in relation to others. No other alterations were observed. In conclusion, we verified that the consumption of the different fatty acids in this experimental model has potential to alter lipoproteins levels but not to iniciate or maintain the inflammatory process associated with atherogenesis.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1973. / Includes bibliographical references (p. 175-181).

A aterosclerose é classificada como enfermidade crônica não transmissível e é considerada uma das principais causas de morte e morbidade em vários países, incluindo o Brasil. Entre as possíveis causas de sua gênese está o hábito alimentar, especificamente o consumo de ácidos graxos, principalmente saturados e trans. Ácidos graxos saturados possuem características biológicas e fisico-químicas diferentes dos insaturados. Os mais abundantes na dieta humana são o palmítico e esteárico. Sua associação com acometimentos cardiovasculares vem sendo cada vez mais investigada, principalmente os que possuem mais de dez carbonos em sua cadeia interferindo no metabolismo de lipoproteínas podendo desencadear todo o processo aterosclerótico. A indústria de alimentos vem desenvolvendo algumas tecnologias opcionais para reduzir ou eliminar ácidos graxos trans, em especial, o elaídico, dentre elas a modificação no processo de hidrogenação que aumenta a quantidade de ácidos graxos saturados. Alguns alimentos industrializados necessitam de uma grande quantidade de ácidos graxos saturados promovendo um aumento no teor de ácido palmítico e esteárico, sendo este último considerado um ácido graxo saturado neutro, mas dependendo da concentração utilizada, pode contribuir no decréscimo da HDL-c (High Density Lipoprotein), dentre outras alterações deletérias. Desta forma, investigar as alterações de determinados parâmetros biológicos diante da mudança da proporção de ácidos graxos saturados, respeitando o teor total de lipídios de uma dieta é a base deste estudo. Foram realizados ensaios em material biológico para a determinação dos seguintes parâmetros: 1) Atividade de enzimas antioxidantes; 2) Peroxidação lipídica em tecidos; 3) Lipidograma; 4) Determinação do perfil de ácidos graxos de tecidos e rações e 5) Expressão de genes relacionados com o processo aterosclerótico (ICAM-1, VCAM-1, CD36 e MCP-1). A determinação da atividade de enzimas antioxidantes foi realizada considerando somente as enzimas Catalase (CAT) e Superóxido Dismutase (SOD), por se tratarem de enzimas com alteração expressiva no processo aterogênico, na ocorrência de disfunção endotelial. Neste trabalho, foi analisada a atividade das referidas enzimas no tecido hepático e cardíaco, onde não foram constatadas alterações. O mesmo processo biológico que estimula a produção excessiva de espécies reativas pode levar ao aumento da peroxidação lipídica, principalmente de ácidos graxos polinsaturados das membranas celulares, em tecidos como fígado, cérebro e coração. A peroxidação lipídica apresentou diferenças significativas no tecido hepático. O grupo alimentado com ração enriquecida com tripalmitato apresentou peroxidação lipídica aumentada em relação ao grupo controle. Correlacionando com o perfil de ácidos graxos do tecido hepático, notamos que houve maior incorporação de ácido palmítico nesse tecido, que por apresentar configuração linear, quando incorporado à membrana celular, pode levar à disfunção e possível suscetibilidade a danos, como a peroxidação. No tecido cardíaco e no tecido cerebral não foram observadas alterações e diferenças entre os tratamentos. O lipidograma consiste na quantificação de lipoproteínas e frações lipídicas, compondo o perfil lipídico no plasma sanguíneo. Os resultados obtidos mostraram que o colesterol total foi significativamente menor no grupo controle, assim como triacilglicerol e LDL colesterol (LDL-c). Já HDL colesterol (HDL-c) está reduzida no grupo que recebeu ração suplementada com ácido palmítico, assim como este grupo apresentou parâmetros aumentados nas dosagens de triacilglicerol e colesterol total. Os grupos alimentados com ração suplementada com triestearato e trioleato apresentaram resultados intermediários para a dosagem de HDL-c, com valores tendendo ao grupo suplementado com tripalmitato. Em relação à dosagem de LDL-c, foi constatada diferença entre os grupos suplementados e o grupo controle. Destaca-se que não houve diferença entre a dosagem entre os grupos suplementados. Portanto, o grupo alimentado com dieta enriquecida com ácido oleico (monoinsaturado) equipara-se aos grupos alimentados com dietas enriquecidas com ácido esteárico e palmítico (saturados). O perfil de ácidos graxos do tecido hepático mostrou uma porcentagem elevada de ácido palmítico no grupo alimentado com ração enriquecida com o mesmo ácido graxo, com diferença estatística em relação aos demais grupos. Já em relação ao ácido esteárico, não houve diferenças significativas entre os grupos. Em compensação, o teor de ácido oleico no grupo suplementado com este mesmo ácido graxo e com ácido palmítico foi significativamente diferente em relação aos demais, com valores superiores. Este resultado demonstra que não houve dessaturação do ácido esteárico a oleico, ao menos neste modelo. No tecido cardíaco, foi observado o mesmo comportamento. No tecido cardíaco não houve diferença estatística significativa da concentração de ácidos graxos, indicando que não houve incorporação ou dessaturação. Ressalta-se que de acordo com determinação realizada utilizando a técnica de cromatografia gasosa, as rações apresentavam em sua composição o teor de lipídios adequado ao modelo animal e as proporções de ácidos graxos alteradas como proposto no objetivo deste trabalho. Em relação às moléculas de adesão e quimiocinas (VCAM-1, ICAM-1, CD-36 e MCP-1) relacionadas com o processo aterosclerótico, houve somente alteração na molécula CD-36 no grupo alimentado com ração enriquecida com trioleato, com redução em relação aos demais. Mas, as moléculas de adesão relacionadas com o processo inicial da aterogênese, a expressão gênica realizada através da técnica de q-RT-PCR não foi relevante, não apresentando diferença entre os tratamentos. Conclui-se, portanto, que os tratamentos aplicados ao modelo animal selecionado possui o potencial de alterar lipoproteínas plasmáticas, mas não de manter a continuidade e desencadear o processo inflamatório relacionado à aterogênese. / Atherosclerosis is chronic a non-communicable disease considered one of a major cause of morbidity and mortality in several countries, including Brazil. Among all the possible causes of their genesis the dietary habit of high fatty acid intake, especially saturated and trans fatty acids is the most important. Saturated and unsaturated fatty acids possess different biological and physicochemical characteristics. The most abundant fatty acid in the human diet are palmitic and stearic and they association with cardiovascular events has been increasingly investigated, especially those one with more than ten carbons in its chain which interfers in the lipoproteins metabolism and can initiate the atherosclerotic process. The food industry has developed some optional technologies to reduce or eliminate the presence of trans fatty acids in foods, in particular elaidic, which after the hydrogenation process increases the saturated fatty acids content. Some industrialized foods requires a large amount of saturated fatty acids that promote an increase of palmitic and stearic content, the last fatty acid mentioned is considered a neutral saturated fatty acid that can contribute to the decrease in HDL-c (High Density lipoprotein), depending on the concentration used, among other deleterious changes. Thus, investigate changes of specifics biological parameters in response to consumption of different saturated fatty acids, respecting the total content of lipids in a normolipidic diet is the aim of this study. Assays were conducted to determine the following parameters in the tissues: 1) Activity of antioxidant enzymes, 2) Lipid peroxidation, 3) Lipidogram; 4) Fatty acid composition 5) Expression of genes related the atherosclerotic process (ICAM-1, VCAM-1, CD36 and MCP- 1). The determination of the activity of antioxidant enzymes was carried out considering only the enzymes Catalase (CAT) and Superoxide Dismutase (SOD), because they are enzymes more sensitive and readily available in changes resulted of an atherosclerotic process with endothelial dysfunction. In the study, no changes were observed in activity of these enzymes in the liver and heart. The same biological process that stimulates the overproduction of reactive species can lead to increased lipid peroxidation, especially of polyunsaturated fatty acids present in cell membranes of tissues such as liver, brain and heart. The group fed with diet enriched with tripalmitate showed increased lipid peroxidation compared to control group. Correlating this information with the fatty acid profile in liver tissue, we noted that there was a greater incorporation of palmitic acid, which exhibit linear configuration when incorporated into the cell membrane and can lead to dysfunction and higher susceptibility to damages such as oxidation. No differences were observed in the others tissues analyzed. The lipidogram is the quantification of lipoprotein and lipid fractions, composing the lipid profile in blood plasma. The results showed that total cholesterol was significantly lower in the control group, as well triglyceride and LDL cholesterol (LDL-c). HDL cholesterol (HDL-C) concentration is reduced and triacylglycerol and cholesterol increased n the group fed with diet supplemented with palmitic. The groups fed with diets supplemented with tristearate and trioleate presented intermediate results for the measurement of HDL-c, with values tending to the group supplemented with tripalmitate. Regarding LDL-c levels, significant differences were observed between the supplemented groups and the control group. Emphasis that there was no difference between the dosage between the supplemented groups. Therefore, the group fed with oleic acid (monounsaturated) supplemented diet equates to the groups fed with diets enriched with stearic and palmitic acid (saturated). The fatty acid profile of liver tissue showed a high percentage of palmitic acid in the group fed with diet enriched with the same fatty acid, with a statistical difference compared to the other groups. In relation to stearic acid, there were no significant differences between groups. As compensation, the oleic acid content in the group supplemented with the same fatty acid and palmitic acid was significantly higher when compared to the others. This result demonstrates that no desaturation of stearic acid to oleic happened in this experimental model. In cardiac tissue there was no statistically significant difference in the concentration of fatty acids, indicating no incorporation or desaturation. Regarding adhesion molecules and chemokines (VCAM-1, ICAM- 1, CD-36 and MCP-1) related to the atherosclerotic process, there was only change in the gene expression of CD-36 molecule in the group fed diet enriched with trioleate, with reduction in relation to others. No other alterations were observed. In conclusion, we verified that the consumption of the different fatty acids in this experimental model has potential to alter lipoproteins levels but not to iniciate or maintain the inflammatory process associated with atherogenesis.

The biggest challenge with magnesium alloy biodegradable implants is the rapid corrosion at the earlier stages of the healing process after implantation. In this research, the impact of surface roughness generated by different means on the corrosion rate of AZ31 magnesium alloy in a simulated biologic environment is investigated. In order to perform accurate experimentation, an in vitro setup is assembled that simulates the human body environment accurately has been prepared using Schinhammer’s in vitro immersion testing setup and Kokubo’s Simulated Body Fluid (SBF). For the immersion test of Mg in SBF, several surface texture groups of Mg have been prepared and submerged into the in vitro tank. The Mg samples’ comparative analysis has been made in terms of corrosion rate, total weight loss and hydrogen gas evolution within a span of 7 days for the first experiment to narrow down the scope and 14 days for the follow up experiment. After 14 days of in vitro immersion test with varying roughness and hydrophobic modifications such as Cytop coating and stearic acid modification, it has been observed that the roughness group created by etching in aqueous NaCl solution for three minutes, shows better corrosion resistance compared to the polished control group. Hydrophobic modifications on the surfaces did not affect the corrosion behavior significantly.

A general discussion of melting and premelting is given. Crystal structures and phase transitions in the C-forms of stearic, palmitic, myristic and lauric acids and in anhydrous sodium stearate are also discussed. Simple theories of infrared and nuclear magnetic resonance spectrometry are presented. Experimental difficulties in the use of solid phase infrared spectra are discussed. A detailed study is made of the temperature behaviour of the infrared spectra of the fatty acids in the region from 750 to 700 cm¯¹ and over the range from about 70ºC below the melting points to about 20ºC above them. Three overlapping peaks of different intensity are resolved - 720 cm¯¹, about 727 cm¯¹, and a peak at higher frequency the position of which varies in the different acids. The complete disappearance of the 720 cm¯¹ band slightly below the melting point in each acid is taken to indicate a transition, not previously reported, to a disordered phase in which there is considerable molecular motion as evidenced by the phase's liquid-like spectra. The presence of three peaks in the region is discussed on the basis of a simple theoretical expression derived by Snyder for the position of fundamental methylene rocking vibrations. The crystallinities of the acids are estimated from an expression, based on the work of Stein and Sutherland, which involves the apparent integrated absorption intensities of the resolved 720 and 727 cm¯¹ bands. The extent of premelting is determined. Extensive premelting giving the spectra a liquid-like, but not completely liquid character is found to take place within about 2ºC of the melting point. The high resolution nuclear magnetic resonance spectra of anhydrous sodium stearate were taken at the limit of their experimental application. The spectra show, however, that the subwaxy, waxy, superwaxy and subneat phases of anhydrous sodium stearate form a structurally similar group (from about 120 to 235ºC) with liquid-crystalline properties, while the neat and melt phases also form a structurally similar group (from 235º C upwards) but with the properties of a liquid. The information indicates extensive premelting beginning in the vicinity of 120ºC, below which temperature the salt is essentially crystalline, which reaches a climax at 235ºC, above which temperature the salt is essentially liquid. / Science, Faculty of / Chemistry, Department of / Graduate

High power impulse magnetron sputtering has shown a lot of promise as a way of depositing photocatalytic thin films of titanium dioxide at low temperatures, however, the films deposited are often amorphous and display uncertain photocatalytic abilities. This thesis explores the deposition and characterization of photocatalytic thin films deposited with high power impulse magnetron sputtering.  Multiple films were deposited with reactive sputtering in both the oxide and metal mode of operations at different temperatures, duty cycles and substrate biases. The crystal structure, microstructure and photocatalytic activity of the samples were then characterized in order to correlate to each other as well as the growth conditions. Crystallinities were determined via a combined use of gracing incidence x-ray diffraction and Raman spectroscopy, microstructures were explored in cross-sectional images taken using scanning electron microscopy and the photocatalytic ability was measured by quantifying the rate constant during degradation of stearic acid while under UV-illumination.  It was found that the crystal structure of the sputtered films was influenced by the deposition mode used: oxide mode depositions yielded an anatase structure while metal mode depositions resulted in rutile or mixed structures. The only crystalline films were formed with substrate heating, the application of bias was found to correlate with the formation of more rutile and the most crystalline films were deposited with a higher duty cycle.  Photocatalytic films were successfully deposited at room temperature, even though they were amorphous. Interestingly, the anatase samples were not found to be the most reactive, instead it was found that the crystal structure only displayed a weak correlation to the reactivity of the films. The findings in this work suggest that the reactivity was also heavily influenced by the surface roughness of the samples as well as their microstructures.

No description available.