Chromium is used in many processing applications, which has led to the formation of chromium(VI) waste. Cr(VI) is an unstable, mobile carcinogen, which is interchangeable with Cr(III) under certain environmental conditions. Management of this waste, however, is often not considered. Mine under investigation is an example of such historic mismanagement. During the second World War, Cr(VI) waste was transferred to the study site from areas where leather products were made for the war effort. This waste was not managed appropriately in the past and with time Cr(VI) leached into the groundwater and possibly surface water resources. As these water resources are used for domestic and agricultural water supply, this may have serious effects on the human and environmental health in the area. Some of the major Cr(VI) effects on human and animal health include malignant tumours, skin irritation, respiratory and reproductive system damage. Lung cancer is of concern when Cr(VI) is inhaled and stomach tumours occur when this chemical pollutant is ingested. The effects of Cr(VI) on plants include the disruption of shoot and root elongation, and if it accumulates enough within the plant can cause ingested health problems for humans and animals. Water quality guidelines state that the Target Water Quality Range for Cr(VI) in drinking water should not exceed 0.05 mg/L. Prolonged exposure of values higher than this target value has adverse health effects and may result in cancer. The study site has a scarcity in water sources and therefore requires good quality water resources. This study aims to identify and use biomarkers to assist in the hydrological characterization of the mine. Available mitigation options can be implemented once it is known how the water in the area moves and distributes Cr(VI) pollution. A biomarker is an indicator of a biological state, which in turn can be used to assist in characterizing the chemical conditions of the sub-surface. Bacteria can aid as environmental biomarkers as they are sensitive and specific to the environmental conditions in which they flourish. In this way they give a good indication of the environmental condition and any possible pollution. Due to the fact that ground- and surface water are integrated resources, it is likely that if one is impacted by pollution, it will indirectly impact the other one. Therefore, the biomarkers identified can be used to characterize water pollutants that are present in ground- and some surface water resources. A description of the study site is provided, wherein the climate, elevation, geology, land use, geohydrology, hydrochemistry and surface water are documented. These factors help to identify and clarify the sources and pathways that water and the pollution would follow. Ten water samples, from surface and groundwater, were obtained in two separate sampling opportunities. The first analysis of the water samples included the determination of the chemical constituents. Two of these constituents analyzed were the total Cr and individual Cr(VI) levels. Six water samples had excessively high Cr values (exceeding the Water Quality Target Range of drinking water and water agricultural use). These values ranged from 0.1 – 3.9 mg/L. The 6 samples with excessive Cr(VI) values were used for the microbial analyses. The microbial analyses consisted of DAPI (4’,6-diamidino-2-phenylindole ) staining, for cell enumeration, and molecular analyses. The molecular analyses included polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE) and sequencing applications concluded in the laboratory. Fifteen bands, representing different organisms, were removed from the DGGE polyacrylamide gel and processed for sequencing. The organisms that were present in the sample were uncultured Cyanobacterium, Sediminibacterium salmoneum, uncultured Bacteroidetes bacterium, uncultured betaproteobacterium, uncultured actinobacterium, uncultured Rhodocyclaceae, uncultured Chloroflexi bacterium and uncultured delta-proteobacterium. According to literature most of these organisms may adapt the ability to either reduce Cr(VI) or resist any effect of Cr(VI) in the environment. Two of the bands were highly unidentified organisms, which means that these organisms have not yet been cultured or identified in any sense. The reason for this is that most microorganisms have not yet been documented. This also makes it difficult to identify the exact bacterial strain present within the samples. The deoxyribonucleic acid (DNA) sequences of the different organisms were very different from each other, when compared by a dendrogram. This means that there was a diverse community present within the samples. Electrical conductivity profiles were conducted in the monitoring boreholes to identify possible fracture positions. The total chromium and chromium(VI) levels were documented and compared. Other chemical factors were analysed and those of high value, such as chloride, nitrate and chromium measurements, were used for statistical analyses and comparison with the biomarkers present in the sample. A positive correlation was found between the sample sites and the organisms present within each. It was noted that different communities have different metabolic activities related to susceptibility and will therefore differ under specific environmental conditions. The microorganisms that were present in the 6 water samples all have the ability to either resist or reduce Cr(VI). This means that in Cr(VI) polluted areas they are more likely to flourish than organisms that do not possess this ability. Such susceptible, non-resistant organisms would otherwise occur naturally in a non-polluted environment. From the obtained results it was noted that microorganisms could aid as biomarkers when determining the environmental condition (with respect to Cr(VI) pollution). The bacteria analysed in the samples all indicate a level of chromium pollution, and aided in the determination of pollution sources. These biomarkers can therefore be used to determine the location of other chromium deposits not yet located. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2013

Chromium is used in many processing applications, which has led to the formation of chromium(VI) waste. Cr(VI) is an unstable, mobile carcinogen, which is interchangeable with Cr(III) under certain environmental conditions. Management of this waste, however, is often not considered. Mine under investigation is an example of such historic mismanagement. During the second World War, Cr(VI) waste was transferred to the study site from areas where leather products were made for the war effort. This waste was not managed appropriately in the past and with time Cr(VI) leached into the groundwater and possibly surface water resources. As these water resources are used for domestic and agricultural water supply, this may have serious effects on the human and environmental health in the area. Some of the major Cr(VI) effects on human and animal health include malignant tumours, skin irritation, respiratory and reproductive system damage. Lung cancer is of concern when Cr(VI) is inhaled and stomach tumours occur when this chemical pollutant is ingested. The effects of Cr(VI) on plants include the disruption of shoot and root elongation, and if it accumulates enough within the plant can cause ingested health problems for humans and animals. Water quality guidelines state that the Target Water Quality Range for Cr(VI) in drinking water should not exceed 0.05 mg/L. Prolonged exposure of values higher than this target value has adverse health effects and may result in cancer. The study site has a scarcity in water sources and therefore requires good quality water resources. This study aims to identify and use biomarkers to assist in the hydrological characterization of the mine. Available mitigation options can be implemented once it is known how the water in the area moves and distributes Cr(VI) pollution. A biomarker is an indicator of a biological state, which in turn can be used to assist in characterizing the chemical conditions of the sub-surface. Bacteria can aid as environmental biomarkers as they are sensitive and specific to the environmental conditions in which they flourish. In this way they give a good indication of the environmental condition and any possible pollution. Due to the fact that ground- and surface water are integrated resources, it is likely that if one is impacted by pollution, it will indirectly impact the other one. Therefore, the biomarkers identified can be used to characterize water pollutants that are present in ground- and some surface water resources. A description of the study site is provided, wherein the climate, elevation, geology, land use, geohydrology, hydrochemistry and surface water are documented. These factors help to identify and clarify the sources and pathways that water and the pollution would follow. Ten water samples, from surface and groundwater, were obtained in two separate sampling opportunities. The first analysis of the water samples included the determination of the chemical constituents. Two of these constituents analyzed were the total Cr and individual Cr(VI) levels. Six water samples had excessively high Cr values (exceeding the Water Quality Target Range of drinking water and water agricultural use). These values ranged from 0.1 – 3.9 mg/L. The 6 samples with excessive Cr(VI) values were used for the microbial analyses. The microbial analyses consisted of DAPI (4’,6-diamidino-2-phenylindole ) staining, for cell enumeration, and molecular analyses. The molecular analyses included polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE) and sequencing applications concluded in the laboratory. Fifteen bands, representing different organisms, were removed from the DGGE polyacrylamide gel and processed for sequencing. The organisms that were present in the sample were uncultured Cyanobacterium, Sediminibacterium salmoneum, uncultured Bacteroidetes bacterium, uncultured betaproteobacterium, uncultured actinobacterium, uncultured Rhodocyclaceae, uncultured Chloroflexi bacterium and uncultured delta-proteobacterium. According to literature most of these organisms may adapt the ability to either reduce Cr(VI) or resist any effect of Cr(VI) in the environment. Two of the bands were highly unidentified organisms, which means that these organisms have not yet been cultured or identified in any sense. The reason for this is that most microorganisms have not yet been documented. This also makes it difficult to identify the exact bacterial strain present within the samples. The deoxyribonucleic acid (DNA) sequences of the different organisms were very different from each other, when compared by a dendrogram. This means that there was a diverse community present within the samples. Electrical conductivity profiles were conducted in the monitoring boreholes to identify possible fracture positions. The total chromium and chromium(VI) levels were documented and compared. Other chemical factors were analysed and those of high value, such as chloride, nitrate and chromium measurements, were used for statistical analyses and comparison with the biomarkers present in the sample. A positive correlation was found between the sample sites and the organisms present within each. It was noted that different communities have different metabolic activities related to susceptibility and will therefore differ under specific environmental conditions. The microorganisms that were present in the 6 water samples all have the ability to either resist or reduce Cr(VI). This means that in Cr(VI) polluted areas they are more likely to flourish than organisms that do not possess this ability. Such susceptible, non-resistant organisms would otherwise occur naturally in a non-polluted environment. From the obtained results it was noted that microorganisms could aid as biomarkers when determining the environmental condition (with respect to Cr(VI) pollution). The bacteria analysed in the samples all indicate a level of chromium pollution, and aided in the determination of pollution sources. These biomarkers can therefore be used to determine the location of other chromium deposits not yet located. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2013

In September 2008 Hurricane Ike hit the Texas Gulf Coast with a force stronger than the category 2 storm at which it was rated. With a 3.8 m (12.5 ft) storm surge, the agricultural industry in the area was devastated. The goal of this research was to determine the length of time required to reduce the salt levels brought by the storm surge to near pre-hurricane levels. To do this, four sets of samples were taken across two years and analyzed for salinity using the saturated paste extract method. The initial salt levels in November 2008 had an electrical conductivity (ECe) of the inundated soils as high as 26.7 dS/m. Fifty-four percent of the soils sampled in the 0-15 cm horizons and 9% in the 15-30 cm horizons of the edge area had an ECe >= 4 dS/m. In the surge area 79% of the soils sampled in the 0-15 cm horizons and 30% in the 15-30 cm horizons had an ECe >= 4 dS/m. In April 2009, 38% of the soils sampled in the 0-15 cm horizons and 13% in the 15-30 cm horizons of the edge area had an ECe >= 4 dS/m. In the surge area 71% of the soils sampled in the 0-15 cm horizons and 39% in the 15-30 cm horizons had an ECe >= 4 dS/m. By December 2009, none of the soils sampled in the edge area had an ECe >= 4 dS/m. In the surge area 21% of the soils sampled in the 0-15 cm horizons and 33% in the 15-30 cm horizons had an ECe >= 4 dS/m. By October 2010, all soils sampled had leached sufficient salts to be classified as non-saline to very slightly saline soils. Utilizing the November 2008 data set, 28 random samples were selected for exchangeable Na percent (ESP) in order to develop the ESP-SAR (Na adsorption ratio) predictive equation, ESP= 1.19(SAR)^0.82. The SAR-ESP relationship is statistically significant (95% confidence level), with a correlation coefficient of 0.964 (df=26).

Fabrication of SWCNT-PMMA and Activated Charcoal- PMMA composites was carried out by the compression moulding technique. Then Mechanical and Electrical properties of the composites were investigated. The morphological studies of composites showed a) good dispersion of fillers and b) good interaction between fillers and matrix. Electrical conductivity of SWCNT-PMMA composites was increased by 9 orders of magnitude (at 0.8 % volume fraction of SWCNT) and that of AC-PMMA composites increased by 16 orders of magnitude (at 17 % volume fraction of AC). The percolation threshold of both composites turned out to be lower compared to the theoretical values. A significant improvement in mechanical properties was obtained ??? particularly in AC-PMMA composites which showed a 400 % improvement in Vickers microhardness ??? raising the polymer matrix abrasion property literally to that of Aluminium alloys (Dobrazanski et al 2006). In conclusion, it is to be noted that Activated Charcoal - PMMA composites have a great potential for cost effective conducting polymer composite production by the use of cheap filler: In addition, the compression moulding technique shows good potential for cost effective fabricating technique for amorphous polymers with high electrical and mechanical properties.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The aim of this work was to determine criteria for management of nutrient solution in the production of runner tips for producing strawberry plug plants and parsley and chives for commercial mixed bunches. Two experiments were carried out at Departamento de Fitotecnia-UFSM using 2.5 dm3 polypropylene pots filled with sand, placed over 0.8m heigh benches and fertigated by drippers. The first experiment was conducted from 13 October 2011 to 10 April 2012, using strawberry mother plants cv. Camino Real and Oso Grande. Plants were fertigated by five electrical conductivities, 0.4, 0.8, 1.2, 1.6 and 2.0 dS m-1, respectively, in a (5 x 2) completely randomized factorial experimental design. Runner tips emitted by mother plants were collected weekly and counted, being discarded those necrotic. It was determined the number of leaves, crown diameter and dry mass. Runner tips from mother plants of each treatment were rooted in polystyrene trays for plug plants production. Forty five days later, crown diameter, number of expanded leaves and shoot and root dry weight of plug plants were determined. At the end of the experiment, mother plants of each treatment were also collected for dry mass determination of plant organs. The second experiment was conducted from September 12 to October 22, 2012, comparing five electrical conductivities of the nutrient solution, 0.5; 1.5; 2.0; 2.5 and 3.0 dS m-1, respectively, and eight cropping arrays. The arrays were formed by planting side by side in each pot transplants of parsley and chives from one cell of the commercial tray (1S+1C), from two cells of parsley and one of chives (2S+1C), one of parsley and two of chives (1S+2C), two of parsley and two of chives (2S+2C) and four monocropping arrays as controls: seedlings from one cell tray of parsley (1S) and one of chives (1C) and two of parsley (2S) and two of chives (2C) per pot. It was used a (5 x 8) completely randomized factorial experimental design. At the end of the experiment, plants of both species were harvested, separated and fresh (MVPA) and dry mass (MSPA) of shoot were determined. It was concluded that electrical conductivities of the nutritive solution in the range between 0.8 and 1.1 dS m-1 for growing strawberry mother plants lead to higher runner tips and plug plants production. Intercropped parsley and chives can be grown using the same nutrient solution at 2.0 dS m-1 for the commercial production of mixed bunches, while an electrical conductivity of 1.6 dS m-1 can be used for monocropped chives production. / O objetivo deste trabalho foi determinar critérios de manejo da solução nutritiva na produção de pontas de estolões para a produção de mudas de morangueiro e de salsa e cebolinha para produção de maços comerciais mistos. Dois experimentos foram realizados no Departamento de Fitotecnia da UFSM em dispositivos formados por bancadas de 0,8 m de altura com vasos de polipropileno de 2,5 dm3 preenchidos com areia e fertirrigados por fitas gotejadoras. O primeiro experimento foi realizado no período de 13 de outubro de 2011 a 10 de abril de 2012, com plantas matrizes de morangueiro das cultivares Camino Real e Oso Grande. As plantas foram fertirrigadas com cinco condutividades elétricas, 0,4; 0,8; 1,2; 1,6 e 2,0 dS m-1, respectivamente, em esquema fatorial (5 x 2) e delineamento inteiramente casualisado. As pontas de estolões emitidas pelas plantas matrizes foram coletadas semanalmente e contadas, sendo descartadas aquelas necrosadas. Foram determinados o número de folhas, o diâmetro de coroa e a massa seca. Pontas de estolões oriundas das plantas matrizes de cada tratamento foram enraizadas em bandejas de poliestireno para produção de mudas com torrão. Aos 40 dias após o enraizamento, foi determinada a taxa de formação de mudas e o diâmetro de coroa, número de folhas expandidas e massa seca da parte aérea e raízes dessas mudas. Ao final do experimento, foram coletadas também plantas matrizes de cada tratamento para determinação da massa seca dos diferentes órgãos. O segundo experimento foi realizado de 12 de setembro a 22 de outubro de 2012, no qual foram comparadas cinco condutividades elétricas, 0,5; 1,5; 2,0; 2,5 e 3,0 dS m-1, respectivamente, e oito arranjos de cultivo. Os arranjos foram formados pelo plantio lado a lado em cada vaso de mudas de salsa e de cebolinha provenientes de um alvéolo das bandejas comerciais (1S+1C); de dois alvéolos de salsa e um alvéolo de cebolinha (2S+1C); de um de salsa e dois de cebolinha (1S+2C); de dois de salsa e dois de cebolinha (2S+2C) e quatro sistemas de cultivos solteiros considerados testemunhas: mudas de um alvéolo de salsa (1S) e um de cebolinha (1C) e dois de salsa (2S) e dois de cebolinha (2C) por vaso. Foi empregado um esquema fatorial (5 x 8) em delineamento DIC. No final do experimento, as plantas de cada uma das duas espécies foram separadas e foi determinada a massa verde (MVPA) e seca (MSPA) da parte aérea. Concluiu-se que condutividades elétricas da solução nutritiva entre 0,8 e 1,1 dS m-1 possibilitam maior produção de pontas de estolões de morangueiro e formação de mudas com torrão. No cultivo consorciado de salsa e cebolinha, é possível o uso de uma mesma solução nutritiva com 2,0 dS m-1 para a formação de maços mistos, podendo a mesma solução ser empregada também no cultivo da salsa solteira. No cultivo solteiro de cebolinha, a C.E de 1,6 dS m-1 deve ser empregada.

Les alliages conducteurs à haute tenue mécanique sont utilisés dans de nombreux domaines tels que le transport, l’énergie et l’industrie électronique. La demande en ces matériaux est croissante. Les alliages Cu-Be constituent à l’heure actuelle les matériaux conducteurs les plus résistants mais posent un problème de toxicité et de coût. Pour proposer une alternative à ces derniers, nous avons étudié des alliages Cu-Mg hypo-eutectiques. Deux voies de synthèse ont été utilisées afin d’obtenir des composites endogènes possédant une combinaison originale de propriétés structurelles et fonctionnelles : le refroidissement conventionnel et la solidification rapide par melt-spinning. Les microstructures obtenues ont en commun la présence d’agrégats eutectiques et diffèrent principalement par la dimension des paramètres métallurgiques tels que la taille de grains et la distance interlamellaire. Les systèmes présentent des forces motrices de transformation de phases importantes conduisant à une précipitation au cours d’un maintien thermique. L’investigation des propriétés mécaniques et électriques des alliages Cu-Mg montre que ces dernières égalent celles des alliages Cu-Be. En complément de l’approche expérimentale, nous avons adapté deux modèles : un modèle thermocinétique pour décrire l’évolution temporelle de la microstructure qui a lieu à haute température et un modèle mécanique permettant de rationaliser l'influence des paramètres microstructuraux sur les propriétés mécaniques et électriques. / Copper-based high strength conductive alloys are used in a myriad of applications such as transport, energy and electronic industries. The demand for these materials is booming. The strongest conductive alloy is based on the Cu-Be system which has the disadvantage of toxicity and cost. In an attempt to find an alternative to these, we have developed hypoeutectic Cu-Mg alloys. Two synthesis routes were applied to produce endogenous compounds with a unique combination of structural and functional properties: the conventional cooling and the rapid solidification by melt-spinning. The obtained microstructures share the presence of eutectic aggregates and differ mainly by the size of the metallurgical parameters such as grain size and interlamellar distance. The two systems provide high driving forces for phase transformations leading to precipitation during aging. The investigation of the mechanical and electrical properties of Cu-Mg alloys shows that they are equal to those of the Cu-Be alloys. In addition to experimental approach, we have adapted two models: a thermo-kinetic one to describe time evolution of the microstructure which takes place at high temperature and a mechanical one to rationalize the influence of microstructural parameters on mechanical and electrical properties.

Le coût de la maintenance aéronautique pourrait être réduit en proposant des stratégies d’inspection « intelligentes » intégrant des outils prédictifs de l’évolution des défauts, comme la vitesse de propagation de la corrosion intergranulaire.Dans cette thèse, nous avons cherché à quantifier les deux modes d’endommagement associés à la corrosion intergranulaire sur un alliage 2024 : la composante « perforante » (dissolution des pointes de joint de grain) et la composante « émoussante » (dissolution des parois des grains dans les cavités intergranulaires). Pour évaluer la composante « perforante », nous proposons une nouvelle variante de la méthode TFP (méthode OTFP) plus complète car elle ne se limite pas à caractériser le défaut le plus rapide mais permet de suivre l’ensemble des défauts perforants grâce à la nature optique de la détection. Dans cette méthode, le dispositif expérimental laisse libre la face de détection, ce qui permet de prélever l’électrolyte issu des cavités intergranulaires et de procéder à son analyse chimique. Cette donnée, peu connue à ce jour, a été utilisée pour valider des modèles de « transport réactif » qui pourront servir de base à des simulations prédictives intégrant l’effet de la nature de l’environnement. La porosité au sein du matériau induite par la corrosion intergranulaire et amplifiée par la dissolution « émoussante » a été suivie en temps réel par mesure de la conductivité électrique avec une sonde à courants de Foucault. D’abord calibrées en régime potentiostatique, ces méthodes se sont par la suite révélées efficaces pour évaluer l’endommagement associé à la corrosion intergranulaire lors d’une corrosion de type atmosphérique. / Costs of aeronautical maintenance can be reduced by implementation of “smart” inspection strategies integrating predictive data on the evolution of defects such as the propagation rate of intergranular corrosion.In this work, intergranular corrosion damage on 2024 aluminium alloy was characterized by two modes : the “perforating” damage (dissolution of the grain boundary tips) and the “blunting” damage (dissolution of the grain walls in the intergranular cavities). To evaluate the “perforating” damage, a new version of the TFP method (OTFP method) which is more complete, was designed. The OTFP method allows to detect all the intergranular corrosion defects and not only the fastest full penetrating grain boundary thanks to the optical nature of the detection. In this method the detection backside of the thin foil is free, which makes possible the collection of the trapped electrolyte in the intergranular cavities to carry out its chemical analysis. This not well-known data, was used to validate “mass-transport” models which could be implemented in predictive simulations considering the effect of the environmental conditions. The porosity inside the foil induced by the intergranular corrosion and enhanced by the “blunting” dissolution was followed in real-time by measuring the electrical conductivity using an eddy current probe.These methods were first calibrated in potentiostatic tests and then successfully applied to evaluate the intergranular corrosion damage in atmospheric corrosion conditions.

Les matériaux hybrides organique/inorganiques ont reçu beaucoup d'attention ces dernières années dans les études des nanomatériaux. En effet, ils possèdent des propriétés physiques et chimiques uniques grâce aux effets synergiques de chaque composant. En particulier, les nanoparticules de silice (SiO2) présentent des caractéristiques intéressantes, comme une bonne stabilité chimique et thermique. Elles peuvent être préparées de différentes tailles et peuvent aussi être facilement fonctionnalisées. Les polymères conducteurs intrinsèques comme le polythiophène et la polyaniline (PANI) peuvent exister sous différents états d'oxydation et donc répondre à des stimuli extérieurs en changeant une de leur caractéristique (couleur, conductivité, etc…). La PANI est un polymère non-toxique, thermiquement stable et peu coûteux avec une conductivité relativement élevée qui a été utilisée comme film antistatique, matériel d'électrode, inhibiteur de corrosion et comme surface sensible de capteur. Depuis la découverte des polymères conducteurs en 1977, plusieurs travaux ont été effectués sur la préparation, la caractérisation et les applications de films polymériques construits à la surface de matériaux comme la silice. Parmi les différents types de composites existants, les particules de type cœur@coquille composées d’un cœur inorganique et d’une couronne de polymère sont les plus prometteurs. Dans cette étude, nous avons donc décidé de travailler sur la synthèse de composites cœur@coquille constitués d’une coquille de PANI et d’un cœur de particules de silice.Dans la littérature, en utilisant des protocoles expérimentaux similaires, deux morphologies très contradictoires ont été obtenues après la polymérisation par oxydation chimique d'aniline en présence de particules de silice : cœur@coquille et framboise (structure inversée avec la PANI comme cœur). Nous avons alors décidé de réexaminer la synthèse de PANI en présence de particules de silice. Pour cela, nous avons, dans un premier temps, synthétisé des particules de silice monodisperses de différentes tailles (300, 160 et 90 nm) par procédé Stöber. Nous avons ensuite réalisé la polymérisation chimique de l'aniline en présence de ces particules de silice dans des conditions contrôlées afin de promouvoir une adsorption des ions aniliniums en surface des particules. Différents paramètres expérimentaux ont été étudiés tels que la température, la concentration en réactifs, la taille des particules… Les résultats en termes de morphologie sont discutés en fonction de ces paramètres. Dans un second temps, nous avons fonctionnalisé la surface des particules de silice par un alcoxysilane afin de favoriser la polymérisation de l’aniline à la surface des particules. Ainsi, nous avons obtenu des structures SiO2@PANI avec une épaisseur de polymère contrôlable. La dernière partie de ce travail traite des premiers essais qui ont été réalisés afin d’utiliser ces composites SiO2@PANi pour des applications environnementales. Deux applications ont notamment été envisagées, l'adsorption de métaux pour l'aspect de particule et la détection de gaz pour les capacités conductrices de la PANI. / Organic/inorganic hybrid materials have received much attention in recent years such as in the field of nano-materials. Indeed, these materials possess unique physical and chemical properties due to the synergistic effect of both components. In particular, silica nanoparticles (SiO2) present interesting properties, such as good chemical and thermal stabilities. They can be prepared in different size and can be easily chemically modified. Intrinsically conducting polymers such as polythiophene and polyaniline (PANI) can exist in different oxidation states and respond to external stimuli by changing one of their characteristics (color, conductivity, …). PANI is a non-toxic, thermally stable and low cost polymer with relatively high conductivity that has been used as antistatic coating, electrode materials, corrosion inhibitor and active layer of sensors. Since the discovery of conducting polymer in 1977, several works have been carried out on the preparation, characterization and applications of polymeric films build on various surfaces like silica. Among the different kinds of composites that exist, inorganic-polymer core-shell nanoparticles are more promising candidates. In this study, we decided to work on the synthesis of core@shell hybrid compounds based on PANI shells and silica nanoparticles cores.In the literature, using similar experimental protocols, two morphologies have been obtained after chemical polymerization of aniline in the presence of silica particles: core@shell and raspberry (inverted structure with PANI as core). We thus decided to reinvestigate the synthesis of PANI in the presence of silica particles. For this, we first synthesized silica particles with different sizes by Stöber process. We then performed the chemical polymerization of aniline in the presence of these naked silica particles under different conditions: temperature, concentration of reactive. However, in all cases, we never managed to obtain core@shell structures. Finally, we succeed in developing a method to prepare these core@shell particles which relies on the functionalization of the SiO2 by alkoxysilanes followed by the polymerization of aniline at room temperature. A series of core-shell particles with tunable PANI thickness has been prepared by this method. The last part of this work deals with the first tests that have been carried out in order to use these composites SiO2@PANi for environmental applications. Two applications have been considered, the adsorption of metals for the particle appearance and the detection of gas for the conductive capacities of the PANI.

Philosophiae Doctor - PhD / One of the most powerful aspects of conducting polymers is their ability to be nanostructured through innovative, synthetically manipulated, transformations, such as to tailor-make the polymers for specialized applications. In the exponentially increasing wide field of nanotechnology, some special attention is being paid to innovative hybrid dendrimer-core based polymeric smart materials. Star copolymers are a class of branched macromolecules having a central core with multiple linear polymer chains extending from the core. This intrinsic structural feature yields a unique 3D structure with extended conjugated linear polymer chains, resulting in star copolymers, which have higher ionic conductivities than their corresponding non-star conducting polymer counterparts. In this study an in-depth investigation was carried out into the preparation and characterization of specialized electronic smart materials. In particular, the preparation and characterization of novel conducting dendrimeric star copolymers which have a central poly(propylene imine) (PPI) dendrimer core with conducting polypyrrole (PPy) chains extending from the core was carried out. This involved, first, the preparation of a series of dendrimeric polypyrrole poly(propylene imine) star copolymers (PPI-co-PPy), using generations 1 to 4 (G1 to G4) PPI dendrimer precursors. The experimental approach involved the use of both chemical and electrochemical synthesis methods. The basic procedure involved a condensation reaction between the primary amine of a diamino functional PPI dendrimer surface and 2-pyrrole aldehyde, to afford the pyrrole functionalized PPI dendrimer (PPI-2Py). Polymerization of the intrinsically contained monomeric Py units situated within the dendrimer backbone was achieved via two distinctly different routes: the first involved chemical polymerization and the second was based on potentiodynamic oxidative electrochemical polymerization. The star copolymers were then characterized using various sophisticated analytical techniques, in-situ and ex-situ. Proton nuclear magnetic resonance spectroscopy (1HNMR) and Fourier transform infrared spectroscopy (FTIR) were used to determine the structures. Scanning electron microscopy (SEM) was used to determine the morphology. Themogravimetric analysis (TGA) was used to study the thermal stability of the prepared materials. X-ray diffraction analysis (XRD) was used to study the structural make-up of phases, crystallinity and amorphous content. Hall effect measurements were carried out to determine the electrical conductivity of the chemically prepared star copolymers. The PPI-co-PPy exhibited improved thermal stability compared to PPI-2Py, as confirmed by TGA. SEM results showed that the surface morphology of the functionalized dendrimer and star copolymer differed. The surface morphology of the chemically prepared star copolymers resembled that of a flaky, waxy material, compared to the ordered morphology of the electrochemically grown star copolymers, which resembled that of whelk-like helixes. In the case the electrochemically grown star copolymers, SEM images recorded at higher magnifications showed that the whelk-like helixes of the star copolymers were hollow tubes with openings at their tapered ends, and had an average base diameter of 2.0 mu;m. X-ray diffraction analysis of the first generation star copolymer G1PPI-co-PPy revealed a broadly amorphous structure associated with PPy, and crystalline peaks for PPI. Cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivity of the star copolymer materials. Electrochemical impedance spectroscopy data showed that the G1PPI-co-PPy exhibited slightly higher ionic conductivity than pristine PPy in lithium perchlorate. The second generation star copolymer G2PPI-co-PPy electrochemically deposited on a platinum (Pt) electrode had a lower electrochemical charge transfer resistance compared to electrodeposited polypyrrole (PPy) on a Pt electrode, and bare Pt. The decrease in charge transfer resistance was attributed to an increase in the conjugation length of the polymer as a result of the linking of the highly conjugated PPy to the PPI dendrimer. Bode impedimetric analysis indicated that G2PPI-co-PPI was a semiconductor, with a maximum phase angle shift of 45.3° at 100 MHz. The star copolymer exhibited a 2- electron electrochemistry and a surface coverage of 99%. Results of Hall effect measurements showed that the star copolymer is a semiconducting material, having a conductivity of 0.7 S cm-1, in comparison to the 1.5 S cm-1 of PPy. To the best of my knowledge, these new star copolymers have not been reported in the open literature. Their properties make them potentially applicable for use in biosensors. / South Africa