Water-in-oil (w/o) microemulsion systems, stabilised by either an anionic surfactant or a cationic surfactant were studied. The anionic system consisted of ethoxylated nonylphenol phosphate esters (Atpol), Shellsol oil and an alcohol. These microemulsions tolerated an increase in ionic strength of the water phase up to a point: Beyond this point no microemulsion could be obtained. However, adding amine salts, e.g. diethanolamine nitrite, improved the emulsification of the aqueous phase. Increasing the alcohol (cosurfactant) chain length up to octanol also increased the uptake of the aqueous phase. Thus octanol yielded the best results in terms of emulsifying large volumes of the water-phase, particularly at high salt concentrations. A key objective was to prepare stable microemulsions with high nitrite content. The maximum microemulsion nitrite contents (expressed as NaNO2equivalent by mass) achieved were: -- About 10% when a 30% NaNO2solution was emulsified -- 23% when neat diethyl ethanolamine nitrite (DEEAN) was solubilized, and -- 23% for mixtures of diethanolamine nitrite (DEtOHAN) and NaNO2 in water. The cationic microemulsion system was based on the double-chain cationic surfactant, didodecyldimethyl ammonium chloride (DDAC). In this case the solubilization of the following acetate salts were investigated: ammonium, sodium, magnesium, zinc and manganese. As with the Atpol system, it was found that increasing the ionic strength is detrimental to microemulsification of the aqueous phase. In the DDAC system, an increase in the alcohol chain length beyond butanol led to reduced aqueous phase uptake. Thus the natures and concentrations of the surfactant and the cosurfactant as well as the ionic strength of the aqueous phase determine the stability and the emulsification of large volumes of aqueous phase. In general there is an optimum ionic strength at which the salt content of the microemulsion formulation is maximised. / Dissertation (MSc (Chemistry))--University of Pretoria, 2007. / Chemistry / unrestricted

The kinetics for radiation induced dissolution of spent nuclear fuel is a key issue in the safety assessment of a future deep repository. Spent nuclear fuel mainly consists of UO2 and therefore the release of radionuclides (fission products and actinides) is assumed to be governed by the oxidation and subsequent dissolution of the UO2 matrix. The process is influenced by the dose rate in the surrounding groundwater (a function of fuel age and burn up) and on the groundwater composition. In this licentiate thesis the effects of HCO3- (a strong complexing agent for UO22+) and ionic strength on the kinetics of UO2 oxidation and dissolution of oxidized UO2 have been studied experimentally. The experiments were performed using aqueous UO2 particle suspensions where the oxidant concentration was monitored as a function of reaction time. These reaction systems frequently display first order kinetics. Second order rate constants were obtained by varying the solid UO2 surface area to solution volume ratio and plotting the resulting pseudo first order rate constants against the surface area to solution volume ratio. The oxidants used were H2O2 (the most important oxidant under deep repository conditions), MnO4- and IrCl62-. The kinetics was studied as a function of HCO3- concentration and ionic strength (using NaCl and Na2SO4 as electrolytes). The rate constant for the reaction between H2O2 and UO2 was found to increase linearly with the HCO3- concentration in the range 0-1 mM. Above 1 mM the rate constant is independent of the HCO3- concentration. The HCO3- concentration independent rate constant is interpreted as being the true rate constant for oxidation of UO2 by H2O2 [(4.4 ± 0.3) x 10-6 m min-1] while the HCO3- concentration dependent rate constant is used to estimate the rate constant for HCO3- facilitated dissolution of UO22+ (oxidized UO2) [(8.8 ± 0.5) x 10-3 m min-1]. From experiments performed in suspensions free from HCO3- the rate constant for dissolution of UO22+ was also determined [(7 ± 1) x 10-8 mol m-2 s-1]. These rate constants are of significant importance for simulation of spent nuclear fuel dissolution. The rate constant for the oxidation of UO2 by H2O2 (the HCO3- concentration independent rate constant) was found to be independent of ionic strength. However, the rate constant for dissolution of oxidized UO2 displayed ionic strength dependence, namely it increases with increasing ionic strength. The HCO3- concentration and ionic strength dependence for the anionic oxidants is more complex since also the electron transfer process is expected to be ionic strength dependent. Furthermore, the kinetics for the anionic oxidants is more pH sensitive. For both MnO4- and IrCl62- the rate constant for the reaction with UO2 was found to be diffusion controlled at higher HCO3- concentrations (~0.2 M). Both oxidants also displayed ionic strength dependence even though the HCO3- independent reaction could not be studied exclusively. Based on changes in reaction order from first to zeroth order kinetics (which occurs when the UO2 surface is completely oxidized) in HCO3- deficient systems the oxidation site density of the UO2 powder was determined. H2O2 and IrCl62- were used in these experiments giving similar results [(2.1 ± 0.1) x 10-4 and (2.7 ± 0.5) x 10-4 mol m-2, respectively]. / QC 20101116

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No description available.

Silicate minerals are the most common mineral group in the earth's crust so it is not surprising that their weathering reactions dominate the chemistry of many earth surface processes. This project used forsterite as a model system to identify the important factors that affect silicate mineral dissolution rates and grain lifetimes in the weathering environment. I determined an empirical rate law for forsterite dissolution of forsterite in oxalic acid solutions: based on a series of 124 semi-batch reactor experiments over a pH range of 0 to 7 and total oxalate concentrations between 0 and 0.35 m at 25°C. These experiments show that oxalate-promoted dissolution rates depend upon both oxalate concentration and pH. I propose a reaction mechanism in which a hydrogen ion and an oxalate ion are simultaneously present in the activated complex for the reaction that releases H4SiO4 into solution. By analogy, I propose that water acts as a ligand in the absence of oxalate. I also ran 82 batch reactor experiments in magnesium and sodium sulfate and magnesium and potassium nitrate solutions. These experiments show that ionic strength up to 12 m, log mMg up to 4 m, and log mSO4 up to 3 m have no effect on forsterite dissolution rates. However, decreasing aH2O slows forsterite dissolution rates. The effect of decreasing dissolution rates with decreasing aH2O is consistent with the idea that water acts as a ligand that participates in the dissolution process.Forsterite dissolution rate data from previously published studies were combined with results from my experiments and regressed to produce rate laws at low and high pH. For pH < 5.05 or and for pH > 5.05 or I then developed a diagram that shows the effect rate-determining variables on the lifetime of olivine grains in weathering environments using these rate laws. / Ph. D.

La dégradation par fretting-corrosion des prothèses de hanche cimentées est l’une des principales causes de réintervention chirurgicale. L’étude du fretting-corrosion est effectuée entre un acier inoxydable 316L, matériau utilisé pour les tiges fémorales, et un polymère PMMA, matériau modèle du ciment chirurgical, dans différentes solutions, plus ou moins proches du liquide physiologique.L’étude a d'abord été réalisée à potentiel libre (OCP) pour être proche des conditions in vivo. L’influence des chlorures et le rôle de l’albumine, principale protéine du liquide physiologique, sur la dégradation du 316L et de sa couche passive sont ainsi évalués.Pour pouvoir obtenir des informations sur le courant de corrosion, des essais sont effectués à potentiel imposé. Le potentiel choisi est proche de la valeur de potentiel pendant fretting : E = -400 mV(ECS). Ce potentiel permet d’observer la transition entre courant cathodique et courant anodique en fonction de la force ionique. Lors d’un essai de fretting-corrosion, l’albumine joue le rôle d’inhibiteur de corrosion.La dégradation du 316L par fretting-corrosion est une combinaison entre l’usure corrosive, due au milieu physiologique contenant des chlorures, et l’usure mécanique. Il existe un terme de synergie entre usures corrosive et mécanique. L’influence de la force ionique et de l’albumine sur ce terme de synergie est aussi quantifiée.La forme de la trace d’usure en “W”, caractéristique du fretting-corrosion, est due à un gradient de pH et à un mécanisme de corrosion proche de la corrosion caverneuse. Une étude à pH global imposé a permis d’estimer les valeurs probables de pH dans et à une courte distance de la zone d’usure. / In case of total hip joint cemented prosthesis, one of the most important causes of reintervention is the degradation induced by fretting-corrosion. The study of fretting-corrosion mechanism is conducted between a 316L stainless steel, the same material as the femoral stem, and a polymer PMMA, a model material for bone cement, in several solutions, more or less close to physiological liquid.First, the study was investigated at Open Circuit Potential (OCP), to be close to the in vivo conditions. The influence of chlorides and the role of albumin, the principal protein in the physiological liquid, on the 316L and its passive layer degradation are evaluated.To obtain some information on corrosion current, experiments are investigated at applied potential. The chosen potential is close to the value of the potential during fretting: E = -400 mV(SCE). Besides, this potential is a threshold potential for anodic and cathodic transition of current as a function of ionic strength. One of the key points is the role of albumin as a corrosion inhibitor in the degradation by fretting-corrosion.The 316L degradation by fretting-corrosion is a combination between corrosive wear, due to the physiological liquid which contains chlorides, and mechanical wear. There is a synergy term between corrosive and mechanical wears. The influence of ionic strength and albumin concentration on this synergy term is also quantified.The shape of the worn area in “W”, typical of fretting-corrosion, is due to a pH gradient and a corrosion mechanism close to crevice corrosion. A study where the global pH of the solution is fixed allows estimating values of pH in and at a short distance from the worn area.

"The effect of bacterial surface biopolymers on bacterial adhesion to surfaces was studied through experiments and modeling. Atomic Force Microscopy (AFM) provided the tool to measure the interaction forces between different bacterial cells and silicon nitride tips under different chemical conditions at a nanoscopic level. Two bacterial strains were considered: Pseudomonas putida KT2442 and Escherichia coli K-12 JM109. This study addressed the following issues: 1) the effect of solution ionic strength and solvent polarity on adhesion between Pseudomonas putida KT2442 and the silicon nitride AFM tip, 2) role of heterogeneity of bacterial surface biopolymers on bacterial adhesion, 3) role of lipopolysaccharides (LPS) on adhesion at three different scales: continuous, batch, and nanoscale, and 4) nature of interactions between E. coli JM109 and a model surface (silicon nitride tip). To address the first issue, formamide, water, and methanol were used to investigate the effect of polarity on surface characteristics of biopolymers on the bacterial surface while a range of salt concentrations between that of water to 1 M KCl were used to study the effect of ionic strength. The adhesion increased with decreasing polarity of the solvent, indicating that the polymers on the bacterial surface are hydrophilic in nature. The adhesion was slightly affected by ionic strength variations up to a concentration of 0.1 M KCl; this may have been due to the fact that the ionic concentration in the solution did not counterbalance the ionic concentration in the biopolymer brush on the bacterial surface. However, a dramatic increase in the adhesion magnitude was observed when the salt concentration increased above 0.1 M KCl. This transition in adhesion with ionic strength from a low to high value induced a transition in the elasticity of the bacterial surface biopolymers. The biopolymer brush layer did change from rigid to soft with increasing the ionic strength. The elasticity was quantified mainly by the use of the freely jointed chain (FJC) model. Our interest in investigating the role of heterogeneity on adhesion developed from the results of the first study. The bacterial surface polymers were thought to be different in their chemical and physical nature since they were found to span a range of segment lengths. Analyzing the adhesion forces for P. putida KT2442 showed that the bacterial surface is heterogeneous. The heterogeneity was evident on the same cell surface and between different cells from the same population. To resolve the third issue, approximately, 80% of the surface LPS of E. coli K-12 JM109 were removed by treating the cells with 100 mM ethylenediaminetetraacetic acid (EDTA). The effect of LPS removal on the adhesion of the cells to the silicon nitride tip was studied in water and phosphate buffered silane (PBS). The adhesion results from the AFM experiments were compared to batch retention experiments with glass as the substratum and column attachment experiments with columns packed with quartz sand. LPS controlled bacterial adhesion to the different surfaces in the study at three scales: batch, continuous, and nano-scale. Finally, the nature of interactions between E. coli JM109 and a model surface (silicon nitride tip) were investigated in solvents of varying polarity (formamide, water, and methanol). The Young’s modulus of elasticity for the bacterial surface was estimated by fitting of the Hertzian model to the force-indentation curves. Young’s modulus values increased as the solvent polarity decreased, indicating a stiffer bacterial surface in lower polarity solvents. The average adhesion force in each solvent was negatively correlated with the dielectric constant of the solvent, suggesting hydrophilic biopolymers. Specific and non-specific interaction forces between the AFM tip and the biopolymers were further characterized by applying a Poisson statistical analysis to the discrete adhesion data. The specific and non-specific interaction forces were the highest in methanol (-4 and -1.48 nN respectively). These values are in accordance with the high adhesion magnitude values measured with AFM in methanol. The results of my different studies emphasized the important role of AFM in studying biological interactions to different surfaces and in characterizing bacterial surface biopolymers."

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo do presente trabalho foi estudar o comportamento dos potenciais superficiais e do perfil de potencial atraves da membrana de eritr ocito em func ao da forca i onica e das cargas superficiais, usando um modelo que leva em conta as cargas el etricas do glicoc alix e das prote&#305;nas citoplasm aticas, al em das cargas superficiais da bicamada lip&#305;dica e os efeitos dos eletr olitos divalentes. Programas espec&#305;ficos em linguagem C foram elaborados para o c alculo desses potenciais, tomando como dados num ericos resultados experimentais de medidas de mobilidade eletrofor etica de eritr ocitos para diferentes valores de forca i onica. Neste c alculo, o metodo para tratamento dos dados eletrofor eticos indicado por Hsu et al.[57] foi inclu&#305;do em nosso modelo. A equac ao de Poisson-Boltzmann nao linear foi resolvida por computac ao num erica, usando o metodo de Runge-Kutta de quarta ordem, obtendo-se os perfis de potencial. Os resultados mostraram que a estimativa da densidade de carga el etrica na superf&#305;cie de c elulas usando a equac ao cl assica de Helmholtz-Smoluchowski conduz a valores que nao conseguem refletir as forcas que regem o comportamento eletrofor etico das mesmas. O presente modelo gerou valores de potenciais superficiais e perfis de potencial para a membrana do eritr ocito bem distintos daqueles obtidos anteriormente para um modelo descrito por uma equac ao de Poisson-Boltzmann linear. Nossos resultados confirmam que a avaliac ao de parametros el etricos superficiais da membrana de eritr ocito, envolvendo dados oriundos de eletroforese, deve incluir c alculos hidrodin amicos al em de eletroest aticos, como sugerido por Hsu et al. [57]. / The aim of present work was to study the behavior of the surface potentials and the potential profile across erythrocyte membrane in function of ionic strength and surface charge, using a model which takes into account electrical charges on glycocalyx and citoplasmatic proteins, in addition surface charges on lipid bylayer and effects due to mono and divalent electrolytes. Programs in C language were build to estimate the surface potentials, and experimental values of electrophoretic mobilities of erythrocytes for different ionic strength were applied. For this calculation, the method indicated by Hsu et al. [57] for treating electrophoretic data was included in our model. The non linear Poisson-Boltzmann equation was solved by numerical computation, using the forth order Range-Kutta method, to give the potential profiles. Results showed that values of electric charge on cellular surface obtained by applying the classical Helmholtz-Smoluchowski equation were not able to represent the forces involved in the electrophoretic behavior of cells. The present model generate values for surface potentials and potential profiles different from those obtained in previous work for a model described by linear Poisson- Boltzmann equation. According to our results, the estimation of surface electric parameters for the erythrocyte membrane from electrophoretic data must ese hydrodynamics and electrostatics calculations, as suggested by Hsu et al. [57]

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo do presente trabalho foi estudar o comportamento dos potenciais superficiais e do perfil de potencial atraves da membrana de eritr ocito em func ao da forca i onica e das cargas superficiais, usando um modelo que leva em conta as cargas el etricas do glicoc alix e das prote&#305;nas citoplasm aticas, al em das cargas superficiais da bicamada lip&#305;dica e os efeitos dos eletr olitos divalentes. Programas espec&#305;ficos em linguagem C foram elaborados para o c alculo desses potenciais, tomando como dados num ericos resultados experimentais de medidas de mobilidade eletrofor etica de eritr ocitos para diferentes valores de forca i onica. Neste c alculo, o metodo para tratamento dos dados eletrofor eticos indicado por Hsu et al.[57] foi inclu&#305;do em nosso modelo. A equac ao de Poisson-Boltzmann nao linear foi resolvida por computac ao num erica, usando o metodo de Runge-Kutta de quarta ordem, obtendo-se os perfis de potencial. Os resultados mostraram que a estimativa da densidade de carga el etrica na superf&#305;cie de c elulas usando a equac ao cl assica de Helmholtz-Smoluchowski conduz a valores que nao conseguem refletir as forcas que regem o comportamento eletrofor etico das mesmas. O presente modelo gerou valores de potenciais superficiais e perfis de potencial para a membrana do eritr ocito bem distintos daqueles obtidos anteriormente para um modelo descrito por uma equac ao de Poisson-Boltzmann linear. Nossos resultados confirmam que a avaliac ao de parametros el etricos superficiais da membrana de eritr ocito, envolvendo dados oriundos de eletroforese, deve incluir c alculos hidrodin amicos al em de eletroest aticos, como sugerido por Hsu et al. [57]. / The aim of present work was to study the behavior of the surface potentials and the potential profile across erythrocyte membrane in function of ionic strength and surface charge, using a model which takes into account electrical charges on glycocalyx and citoplasmatic proteins, in addition surface charges on lipid bylayer and effects due to mono and divalent electrolytes. Programs in C language were build to estimate the surface potentials, and experimental values of electrophoretic mobilities of erythrocytes for different ionic strength were applied. For this calculation, the method indicated by Hsu et al. [57] for treating electrophoretic data was included in our model. The non linear Poisson-Boltzmann equation was solved by numerical computation, using the forth order Range-Kutta method, to give the potential profiles. Results showed that values of electric charge on cellular surface obtained by applying the classical Helmholtz-Smoluchowski equation were not able to represent the forces involved in the electrophoretic behavior of cells. The present model generate values for surface potentials and potential profiles different from those obtained in previous work for a model described by linear Poisson- Boltzmann equation. According to our results, the estimation of surface electric parameters for the erythrocyte membrane from electrophoretic data must ese hydrodynamics and electrostatics calculations, as suggested by Hsu et al. [57]

Orientadores: Rosiane Lopes da Cunha, Angelo Luiz Fazani Cavallieri / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-12T20:41:04Z (GMT). No. of bitstreams: 1 Kuhn_KatiaRegina_M.pdf: 7905383 bytes, checksum: d2611d08a267478c25b7976ba7ea4940 (MD5) Previous issue date: 2009 / Resumo: Biopolímeros, como as proteínas e os polissacarídeos, são utilizados pela indústria de alimentos por desempenharem um papel essencial na estrutura, textura e estabilidade dos produtos. O entendimento das interações biopoliméricas é importante para melhorar suas propriedades funcionais, como por exemplo, a capacidade de gelificação, e para o desenvolvimento de novos produtos. Sendo assim, este trabalho teve como objetivo estudar as interações macromoleculares de sistemas contendo proteínas do soro de leite (WPI) e/ou polissacarídeo da linhaça (FG) em sistemas gelificados a frio pela adição de sais de cálcio ou sódio, buscando correlacionar estas interações com as propriedades mecânicas e de estrutura dos géis formados. Inicialmente realizou-se a caracterização reológica do polissacarídeo da linhaça e foi observado um comportamento de fluido pseudoplástico e propriedades de gel fraco. Com a adição de sais, verificou-se uma redução na viscosidade intrínseca e nos módulos elástico e viscoso das soluções. Em uma segunda etapa, foram estudados géis puros de WPI (5, 6, 7, 8 e 9% m/m) formados pela difusão de sais de cálcio ou sódio através de membranas de diálise e observou-se a formação de estruturas opaca e translúcida, sendo que o aumento na concentração de WPI levou a uma diminuição na claridade e porosidade dos géis e a um aumento na rigidez, elasticidade e capacidade de retenção de água, em ambos os sistemas (CaCl2 e NaCl). Os géis de WPI formados pela difusão de sais de cálcio apresentaram-se mais rígidos e elásticos, menos deformáveis e com menor capacidade de retenção de água em relação aos géis de sódio. Por último, foram estudados sistemas mistos WPI (8% m/m) ¿ FG (0,1; 0,3 e 0,5% m/m) utilizando dois procedimentos para incorporação de sais, a difusão através de membranas de diálise e a adição direta, e observou-se que o método de preparo dos géis levou a sistemas com propriedades mecânicas bastante distintas. No método de difusão lenta de sais, visualizou-se a formação de géis heterogêneos (separação de fases macroscópica). Nestes sistemas, o aumento na concentração de FG levou a diminuição da rigidez, deformabilidade e da capacidade de retenção de água dos géis como conseqüência da incompatibilidade termodinâmica entre os biopolímeros e descontinuidade da estrutura da rede do gel. No entanto, foi no método de adição direta de sais de sódio que obteve-se os géis bipoliméricos mais fortes, sendo este método o mais indicado visando melhor estrutura e propriedades mecânicas dos géis formados com maior viabilidade de uso em escala industrial / Abstract: Biopolymers, such as proteins and polysaccharides, are used by the food industry for playing an essential role in the structure, texture and stability of the products. An understanding of the biopolymers interactions is important for improvement of their functional properties, such as gelation, and for the new products development. Thus, the aim of this work it was to study macromolecular interactions between whey protein isolate (WPI) and/or flaxseed gum (FG) at cold-set gels formed by calcium or sodium salts addition, by correlation of these interactions with the mechanical properties and structure of the formed gels. Initially, flaxseed gum rheological characterization was realized and it was observed a shear thinning behavior and ¿weak gel¿ properties. Salts addition led to a decrease in intrinsic viscosity and in the storage and loss modulus of solutions. In a second step of this work, pure WPI gels (5, 6, 7, 8 and 9% w/w) formed by calcium or sodium salts diffusion through dialysis membranes were studied and it was observed the formation of structures opaque and translucent, where the increase WPI concentration led to a decrease in the clarity and porosity of the gels and to an increase in hardness, elasticity and water-holding capacity, in both systems (CaCl2 and NaCl). WPI gels formed by calcium salts diffusion were harder and more elastic, less deformable and with lesser ability to hold water in relation to sodium gels. Finally, mixed WPI (8% w/w) ¿ FG (0.1, 0.3 and 0.5% w/w) systems using two procedures for incorporation of salts were studied, the diffusion through dialysis membranes and the direct addition, and it was observed that the gels preparation method led to systems with quite different mechanical properties. By slow salts diffusion, it was observed the heterogeneous gels formation (macroscopic phase separation). In these systems, the increase FG concentration led to a decrease of the hardness, deformability and water-holding capacity of the gels as a consequence of the thermodynamic incompatibility between biopolymers and gel network discontinuity. However, it was by sodium salts direct addition that it were obtained stronger bi-polymeric gels, being this the most appropriate method to better structure and mechanical properties of the formed gels with higher viability for use in industrial scale / Mestrado / Mestre em Engenharia de Alimentos