O processo de absorção do CO2 em soluções aquosas de alcanolaminas foi estudado em uma coluna de parede molhada empregando-se uma tela metálica, de 28 mesh, como promotor de película e operando em contracorrente. As alcanolaminas testadas nos diferentes experimentos foram: monoetanolamina (MEA), 2-amino-2-metil-1-propanol (AMP) e piperazina (PZ). Os experimentos de absorção foram realizados nas soluções aquosas individuais da MEA e AMP; e, nas misturas MEA:AMP e AMP:PZ; visando avaliar a velocidade de absorção do CO2 em diferentes vazões do líquido, a saber: 3.10-7, 6.10-7 e 10.10-7 m3/s. O presente sistema de absorção foi caracterizado através da determinação dos principais parâmetros de transferência de massa: área interfacial efetiva, coeficiente de transferência individual da fase gasosa e o coeficiente volumétrico global médio de transferência de massa. Determinou-se a área interfacial efetiva da coluna, por meio da absorção do CO2 diluído em ar em uma solução aquosa de NaOH, para as diferentes vazões de líquido, sendo os resultados obtidos igual a 106, 126 e 144 m2/m3, respectivamente. O coeficiente volumétrico de transferência de massa da fase gasosa foi determinado por meio da absorção de SO2 diluído em ar em uma solução aquosa de NaOH. Os resultados experimentais mostram que o coeficiente volumétrico individual de transferência de massa e a área interfacial são função da vazão do líquido. As velocidades de absorção do CO2 diluído em ar, em soluções de aminas e suas misturas foram determinadas experimentalmente para diferentes vazões de líquido, sendo os resultados expressos na forma de coeficientes globais de transferência de massa e parâmetros cinético-difusivos da fase líquida. As velocidades de absorção em MEA são bem superiores aos de AMP e NaOH. No caso das misturas foram obtidas velocidades superiores em comparação às das aminas individuais. A velocidade de absorção em AMP é fortemente incrementada na presença de PZ, mesmo em baixa concentração. / The CO2 absorption process in alkanolamine aqueous solutions was studied in a wetted wall column employing a film promotor of thin stainless steel woven wire, 28 mesh, which was operated in countercurrent. The tested alkanolamines were monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ). The absorption experiments were performed in individual aqueous solutions of MEA and AMP and the mixtures MEA:AMP and AMP:PZ, with the aim of evaluating the CO2 absorption rate in different liquid flow rates, namely: 3.10-7, 6.10-7 e 10.10-7 m3/s. This absorption system was characterized through determining of the main parameters of mass transfer: effective interfacial area, individual mass transfer coefficient of the gas phase and the average overall mass transfer volumetric coefficient. The effective interfacial area was determined by the absorption of CO2 diluted in air into an aqueous solution of NaOH for the different liquid flow rates, and the results obtained are 106, 126 and 144 m2/m3, respectively. The mass transfer volumetric coefficient of the gas phase was determined by chemical method of the absorption of SO2 diluted in air into an aqueous solution of NaOH. The experimental results show that the individual mass transfer coefficient and interfacial area are a function of liquid flow rate. On the other hand, the results of the performance of CO2 absorption into amine aqueous solutions were expressed in function of the average overall mass transfer volumetric coefficient and liquid phase diffusive kinetic parameters, which were measured experimentally for different liquid flow rates. The absorption rate in MEA are higher in comparison with AMP and NaOH. In the case of the blended, the absorption rate in AMP is enhanced by piperazine, even in low concentration.

Investigate the interaction of nanomaterials with biological systems, known as nano-bio interaction is of great interest for the assessment of the concern arising from nanomaterials progressive use. Such interaction determines nanomaterials potential effect on human and environment becomes more and more important to understand how they interact with living organisms and the environment. The novel physicochemical characteristics of nanomaterials, such as their small size, large surface area to volume ratio and surface energy, may initiate new toxicological effects due to nanomaterials ability to enter into the biological systems through adsorption and dissolution and modify the structure of various macromolecules An example of these interactions is the adsorption of proteins on nanoparticles surface forming what is known as the 'protein corona'. Therefore, being able to understand how these molecules and other biologically important species are adsorbed and interact, should help us to reduce any adverse impacts of nanoparticles on human health and the environment. Due to the importance of surface composition and surface functionality in nanotoxicology, analytical tools that can probe the change in the structure and composition of the nanoparticles in aqueous media are crucial but remain limited. Therefore in this work, in situ characterization of the liquid–solid interface to probe surface adsorption of environmentally and biologically relevant media on nanoparticle surfaces has been conducted. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy provides the molecular information that allows for the determination of the adsorption mode such as conformational and structural changes of the coordinating ligand. Surface adsorption of titanium dioxide (TiO2) nanoparticles have been investigated in different biological media typically used for toxicity studies and show that the surface composition of TiO2 nanoparticles depends to a large extent on the composition of the medium due to surface adsorption. Moreover, hydrodynamic diameter and surface charge of TiO2 NPs were evaluated using dynamic light scattering DLS. The results indicated that TiO2 NPs undergo different trends in aggregation upon the adsorption of biological media on its surface and zeta potential measurements showed surface charge alterations which are consistent with the aggregation study. In order to understand the dynamic transformations of nanomaterials in biological environments, the effect of dissolution has been predicted. Copper oxide CuO and zinc oxide ZnO nanoparticles were used to study dissolution due to their instability in biological media. Once these particles exposed to solutions they release their ions and tend to aggregate. Therefore, the dissolution of these materials was conducted at size ca. 24 nm and nanoparticles coated with proteins and humic acid employing simulated lung fluids as models to develop a better understanding of how these properties effect the solubility and stability in biological systems. From this study, it was found that both copper oxide and zinc oxide NPs showed different trends in dissolution. Cu and Zn ions once coated with proteins and HA highly dissolved in ALF at low pH 4.5 compared with other fluids (Gamble’s solution and water) at extracellular pH which shows only slightly enhanced in the basal condition. The acidity of ALF may explain the higher solubility of metals that are phagocytized versus those that remain extracellular. Some general conclusions can be drawn from these investigations. It seems that analytical tools to characterize the interfacial region between nanopaerticles and these complex systems provide a reasonably good qualitative and quantitative description of the interactions.

Reactions of aqueous Fe(II) with Fe and Mn oxides influence heavy metal mobility, transformation of trace organics, and important elemental cycles as Fe precipitates form or dissolve, and as electrons move between aqueous and solid phases. Our objective was to characterize reactions of Fe(II) with important metal oxides, using a suite of complementary tools to investigate the extent and underlying mechanisms of Fe(II)-metal oxide redox activity. Nanoscale materials (1-100 nm) may have fundamentally different surface or electronic properties than larger solids. Goethite was synthesized with primary particle dimensions above or below the nanoscale. Despite large differences in particle surface area, goethite nanorods and microrods had similar net Fe(II) sorption and electron transfer properties. Experimental evidence suggested particle aggregation resulted in particle complexes of a similar size, meaning considerations of available reactive surface area could explain our results. Kinetics and extent of Fe(II)-Fe(III) redox reactions between aqueous Fe(II) and goethite were examined using a stable isotope tracer approach. Aqueous Fe(II) that had been enriched in 57Fe was mixed with isotopically-normal goethite. Convergence of Fe isotope ratios in aqueous and solid phases to values predicted by complete Fe atom exchange provided evidence that all goethite Fe(III) atoms could eventually react with Fe(II), despite no evidence for complete atom exchange from bulk measurements of the aqueous or solid phase. Fe isotope data at different experimental conditions was combined with theoretical considerations governing electron transfer in goethite to provide evidence for redox-driven atom exchange involving bulk conduction of electrons between spatially distinct Fe(II) sorption and release sites. Procedures for stable Fe isotope tracer studies have been adapted to investigate redox transformations of magnetite solids with different divalent cation content. Evolution of aqueous Fe(II)-Mn(IV) redox reactions was examined using complementary techniques. After pyrolusite particles were exposed to aqueous Fe(II), aqueous Fe and Mn were analyzed, and X-ray diffraction was utilized with electron microscopy to assess solid phase evolution during continued exposure to Fe(II). Selective use of Fe isotopes during Fe(II) resuspensions allowed us to track chemical changes occurring to one particular Fe addition using 57Fe Mössbauer spectroscopy.

As carbon dissolution rates have been determined for a few chars only, a systematic and comprehensive study was undertaken in this project on the dissolution behaviour of carbon from non-graphitic materials into liquid iron. In addition to measuring the kinetics of carbon dissolution from a number of coal chars into liquid iron as a function of parent coal and coal ash composition, the influence of chemical reactions between solute/solid carbon and ash oxides was also investigated. These studies were supplemented with investigations on one metallurgical coke for the sake of comparison. The wettability of coal chars and coke with liquid iron at 1550 degrees C was measured as a function of time. Being essentially non-wetting, only a marginal improvement in contact angles was observed with time. The accumulation of alumina at the interface was detected for all materials and was seen to increase with time in all cases. Calcium and sulphur also appeared to preferentially accumulate at the interface, concentrating at levels in excess of those expected from the ash composition alone. Despite the high levels of silica in the ash initially, very little silica was detected in the interfacial region, implying ongoing silica reduction reactions. A small amount of silicon was however detected in the iron droplets, indicating silica reduction with solute carbon. It was identified that the reduction reactions can also consume solute carbon in the liquid iron. As this is occurring simultaneously with carbon dissolution into liquid iron, the interdependency of silica reduction and carbon dissolution could potentially limit the observed carbon dissolution rate. A theoretical model was developed for estimating the interfacial contact area between chars and liquid iron. Wettability was found to have a very significant effect on the area of contact. A two-step behaviour was observed in the carbon dissolution of two chars and coke. Slow rates of carbon dissolution in stage II were attributed to very high levels of interfacial blockage by reaction products leading to much reduced areas of contact between carbonaceous material and liquid iron. The first order dissolution rate constants for four chars/coke and the observed trend in first order dissolution rate constants were calculated. These dissolution results compare well with the previously measured dissolution rate constants. The trends in dissolution can be adequately explained on the basis of carbon structure, silica reduction, sulphur concentration in the metal and ash impurities.

Copolymers are used to increase the interfacial strength of immiscible components and suppress recombination of the minor phase by steric hindrance. The experiments conducted in these studies are designed to investigate in situ polymer loop formation at soft interfaces and functionalized nanotube surfaces. Block copolymers are the most effective type of copolymer for compatibilization because they extend perpendicular to the interface, allowing good entanglement with the homopolymer chains. Multiblock copolymers are more effective than diblock copolymers for strengthening the interface because they can cross the interface multiple times, forming “loops” in each phase that provide entanglement points for the homopolymer. The first part of this dissertation focuses on understanding how telechelic variables influence their effectiveness to compatibilize an immiscible polystyrene (PS)/polyisoprene (PI) homopolymer blend. A fast reacting anhydride and amine telechelic pair (Anh-PS-Anh/NH2-PI-NH2) are compared with a slower reacting epoxy and carboxylic acid pair (Epoxy-PS-Epoxy/COOH-PI-COOH). Different molecular weight pairs are used to investigate the influence of end group concentrations and steric effects. We also investigate how the loading level affects the conversion of one telechelic pair. The PI telechelic has a fluorescent tag, which enables gel permeation chromatography (GPC) with fluorescence detection to be used for determining the amount of tagged PI converted and the molecular weight of the copolymer formed in situ as a function of mixing time. The effectiveness of these telechelic pairs as compatibilizers is quantified by annealing the samples and using scanning electron microscopy (SEM) to measure the domain size of the minor phase as a function of annealing time. The second part of this study investigates the grafting of polymer loops to carboxylated multiwall nanotube (COOH-MWNT) surfaces and determining the reaction rate. These polymer loops will improve the nanotube dispersion by steric hindrance and improve energy transfer by creation of polymer chain entanglements. Fourier transform infrared spectroscopy (FT-IR) is used as a novel technique to measure the quantity of Epoxy-PS-Epoxy grafted to the nanotube surface. In addition, we determined the fraction of telechelics that form loops by further reacting the grafted nanotubes with monocarboxy terminated poly(4-methylstryrene) (COOH-P4MS), which only reacts with unbound Epoxy-PS-Epoxy chain ends.

With the rise of nanotechnology in the last decade, nanofluidics has been established as a research field and gained increased interest in science and industry. Natural aqueous nanofluidic systems are very complex, there is often a predominance of liquid interfaces or the fluid contains charged or differently shaped colloids. The effects, promoted by these additives, are far from being completely understood and interesting questions arise with regards to the confinement of such complex fluidic systems. A systematic study of nanofluidic processes requires designing suitable experimental model nano – channels with required characteristics. The present work employed thin liquid films (TLFs) as experimental models. They have proven to be useful experimental tools because of their simple geometry, reproducible preparation, and controllable liquid interfaces. The thickness of the channels can be adjusted easily by the concentration of electrolyte in the film forming solution. This way, channel dimensions from 5 – 100 nm are possible, a high flexibility for an experimental system. TLFs have liquid IFs of different charge and properties and they offer the possibility to confine differently shaped ions and molecules to very small spaces, or to subject them to controlled forces. This makes the foam films a unique “device” available to obtain information about fluidic systems in nanometer dimensions. The main goal of this thesis was to study nanofluidic processes using TLFs as models, or tools, and to subtract information about natural systems plus deepen the understanding on physical chemical conditions. The presented work showed that foam films can be used as experimental models to understand the behavior of liquids in nano – sized confinement. In the first part of the thesis, we studied the process of thinning of thin liquid films stabilized with the non – ionic surfactant n – dodecyl – β – maltoside (β – C₁₂G₂) with primary interest in interfacial diffusion processes during the thinning process dependent on surfactant concentration 64. The surfactant concentration in the film forming solutions was varied at constant electrolyte (NaCl) concentration. The velocity of thinning was analyzed combining previously developed theoretical approaches. Qualitative information about the mobility of the surfactant molecules at the film surfaces was obtained. We found that above a certain limiting surfactant concentration the film surfaces were completely immobile and they behaved as non – deformable, which decelerated the thinning process. This follows the predictions for Reynolds flow of liquid between two non – deformable disks. In the second part of the thesis, we designed a TLF nanofluidic system containing rod – like multivalent ions and compared this system to films containing monovalent ions. We presented first results which recognized for the first time the existence of an additional attractive force in the foam films based on the electrostatic interaction between rod – like ions and oppositely charged surfaces. We may speculate that this is an ion bridging component of the disjoining pressure. The results show that for films prepared in presence of spermidine the transformation of the thicker CF to the thinnest NBF is more probable as films prepared with NaCl at similar conditions of electrostatic interaction. This effect is not a result of specific adsorption of any of the ions at the fluid surfaces and it does not lead to any changes in the equilibrium properties of the CF and NBF. Our hypothesis was proven using the trivalent ion Y3+ which does not show ion bridging. The experimental results are compared to theoretical predictions and a quantitative agreement on the system’s energy gain for the change from CF to NBF could be obtained. In the third part of the work, the behavior of nanoparticles in confinement was investigated with respect to their impact on the fluid flow velocity. The particles altered the flow velocity by an unexpected high amount, so that the resulting changes in the dynamic viscosity could not be explained by a realistic change of the fluid viscosity. Only aggregation, flocculation and plug formation can explain the experimental results. The particle systems in the presented thesis had a great impact on the film interfaces due to the stabilizer molecules present in the bulk solution. Finally, the location of the particles with respect to their lateral and vertical arrangement in the film was studied with advanced reflectivity and scattering methods. Neutron Reflectometry studies were performed to investigate the location of nanoparticles in the TLF perpendicular to the IF. For the first time, we study TLFs using grazing incidence small angle X – ray scattering (GISAXS), which is a technique sensitive to the lateral arrangement of particles in confined volumes. This work provides preliminary data on a lateral ordering of particles in the film. / Mit dem Heranwachsen der Nanotechnologie in den vergangenen zehn Jahren hat sich die Nanofluidik als Forschungsbereich etabliert und erfährt wachsende Aufmerksamkeit in der Wissenschaft, sowie auch in der Industrie. Im biomedizinischen Bereich, wo intrazelluläre Prozesse häufig komplexer, nanofluidischer Natur sind, wird sich vermehrt für ein detailliertes Verständnis von nanofluidischen Prozessen interessiert, z.B. für den Einfluss von Kolloiden verschiedenster Form oder elektrischer Ladung auf die Kanäle und auf das Fließverhalten oder die Auswirkungen der Einengung von Flüssigkeiten und Kolloiden in Nanometer Geometrien. In der vorliegenden Arbeit werden dünne flüssige Filme, hinsichtlich ihrer Funktion als nanofluidische Modelle untersucht. Im ersten Teil der Arbeit wurde die Fließgeschwindigkeit des Fluids aus dem dünnen Film, abhängig von der Konzentration der filmstabilisierenden Tensidmoleküle n – Dodecyl β – D – Maltoside ( β – C₁₂G₂) bei einer konstanten Elektrolytkonzentration von 0.2 mM NaCl untersucht. Mit einem theoretischen Modell konnte das Dünnungsverhalten nachgezeichnet werden. Es wurde eine kritische Tensidkonzentration gefunden, unter der die Oberflächen lateral mobil sind und über der sie sich wie fest verhalten. Dadurch konnten wir Aufschluss darüber erlangen, wie die Oberfläche des Films unter verschiedenen Bedingungen geschaffen ist, und das in Bezug zur Verteilungsdichte der Moleküle an den Oberflächen setzen. Im weiteren wurden komplexere, nanofluidische Systeme untersucht, wobei zum einen ~ 1 nm lange, stäbchenförmige, multivalent geladene Spermidin - Moleküle die punktförmigen Elektrolyte ersetzten. Es konnte eine deutliche Veränderung der Stabilität zwischen Filmen mit und ohne Stäbchen festgestellt werden. Die Filme, mit NaCl, blieben länger in dem metastabilen „Common Film“ (CF) Zustand als die Filme, die eine vergleichbare Konzentration von Spermidin Stäbchen beinhalteten. Die Ergebnisse deuteten auf eine zusätzliche Anziehungskraft durch Brückenbildung zwischen zwei geladenen Oberflächen durch gegensätzlich geladene Stäbchenförmige Moleküle hin. Es konnte gezeigt werden, dass dieser Effekt weder ein Ergebnis von spezifischer Ionenadsorption an die Filmoberfläche war, noch ein Unterschied in den Gleichgewichtszuständen von den Dicken der CFs und der Newton Black Films (NBFs) hervorrief, was auf die korrekte Annahme der Ionenstärke in der Lösung schließen ließ. Auch in Versuchen mit ebenfalls trivalenten Ionen YCl3 wurde festgestellt, dass kein vergleichbarer Überbrückungseffekt auftritt. Die Ergebnisse wurden mit theoretischen Simulationen verglichen und es wurde eine quantitative Übereinstimmung gefunden bezüglich der Größe des Systeminternen Energiegewinns durch den Überbrückungseffekt. Desweiteren wurde das Fließverhalten von Fluiden mit Kolloiden eingeengt in Nanometer Geometrien untersucht. Für zwei verschiedene Arten von Nanopartikeln (Fe3O4 stabilisiert mit Oleinsäure und polymerstabilisierte Goldpartikel) wurde eine Verlangsamung der Fließgeschwindigkeit festgestellt. Mit einem theoretischen Modell konnte das Fließverhalten nur für enorm erhöhte Viskositätswerte des Fluids erklärt werden. Die Viskositätserhöhung wurde mit Partikelaggregaten, die den Ausfluss behindern, erklärt und diskutiert, unter der Annahme eines nicht - Newtonischen Fließverhaltens der Dispersionen. Gleichermaßen wurde die strukturelle Anordnung der Partikel in den Filmen hinsichtlich ihrer vertikalen und lateralen Verteilung untersucht. In dieser Arbeit werden vorläufige Ergebnisse präsentiert, die noch weiteren Studien bedürfen. Mit Neutronenreflexion sollte die Anordnung der Partikel orthogonal zur Oberfläche im Film analysiert werden. Eine qualitative Analyse lässt schließen, dass bei einer höheren Konzentration von Partikeln in Lösung, sich auch eine erhöhte Konzentration von Partikeln im dünnen Film befindet. Leider konnten die Daten nicht hinsichtlich der Lage der Partikel analysiert werden. Zum ersten Mal wurden dünne flüssige Filme mit Kleinwinkelröntgenstreuung unter streifendem Einfall (GISAXS) analysiert. Mit Hilfe dieser Methode sollte eine laterale Anordnung der Partikel im Film untersucht werden. Es konnten erfolgreiche Messungen durchgeführt werden und mit Hilfe der rechnergestützten Analyse konnte eine Aussage gemacht werden, dass ~ 6 nm große Teilchen in ~ 43 nm Abstand sich im Film befinden. Die Aussage bezüglich der kleinen Teilchen könnte sich auf einzelne, kleinere Partikel beziehen, allerdings könnten auch die 43 nm eine relevante Strukturgröße darstellen, da es in der Dispersion gehäuft Aggregate mit dem Durchmesser in dem Größenbereich vorliegen. Zusammenfassend können sich mit dieser Arbeit die dünnen flüssigen Filme als eine wichtige Kernmethode der Untersuchung von nanofluidischen Prozessen, wie sie häufig in der Natur vorkommen, behaupten.

Admixtures like reactants and byproducts are solublenon-crystallizing compounds that can be present in industrialsolutions and affect crystallization of the main substance.This thesis provides experimental and molecular modellingresults on the influence of admixtures on crystal nucleation ofvanillin (VAN). Seven admixtures: acetovanillone (AVA),ethylvanillin (EVA), guaiacol (GUA), guaethol (GUE), 4-hydroxy-acetophenone (HAP), 4-hydroxy-benzaldehyde (HBA), andvanillic acid (VAC) have been used in this study. Classicalnucleation theory is used as the basis to establish arelationship between experimental induction time andsupersaturation, nucleation temperature, and interfacialenergy. A novel multicell device is designed, constructed, andused to increase the experimental efficiency in thedetermination of induction times by using 15 nucleation cellsof small volumes simultaneously. In spite of the largevariation observed in the experiments, the solid-liquidinterfacial energy for each VAN-admixture system can beestimated with an acceptable statistical confidence. At 1 mole% admixture concentration, the interfacial energy is increasedin the presence of GUA, GUE, and HBA, while it becomes lower inthe presence of the other admixtures. As the admixtureconcentration increases from 1 to 10 mole %, the interfacialenergy also increases. The interfacial energies obtained are inthe range 7-10 mJ m-2. Influence of admixtures on metastable zone widthand crystal aspect ratio of VAN is also presented. Theexperimental results show that the admixtures studied arepotential modifiers of the nucleation of VAN. Molecularmodelling by the program Cerius2 is used to identify the likelycrystal growth faces. Two approaches, the surface adsorptionand the lattice integration method, are applied to estimatequantitatively the admixture-crystal interaction energy on thedominating crystal faces of VAN,i.e., {0 0 1} and {1 0 0}. However, a simple and clearcorrelation between the experimental values of interfacialenergy and the calculated interaction energies cannot beidentified. A qualitative structural analysis reveals a certainrelationship between the molecular structure of admixtures andtheir effect on nucleation. The determination of the influenceof admixtures on nucleation is still a challenge. However, themolecular and crystal structural approach used in this thesiscan lead to an improved fundamental understanding ofcrystallization processes. Keywords: Crystallization,nucleation, vanillin, admixtures, additives, impurities,induction time, interfacial energy, molecular modelling,interaction energy.

The aim of the present investigation is to increase theunderstanding of the role played by the solvent in inhibitingor enhancing crystal growth. Drowning-out crystallizationexperiments has been performed by the controlled addition ofwater or ethanol water mixtures to a saturated solution ofbenzoic acid in ethanol-water mixtures. Crystal habitcontrolling factors have been identified.Seededcrystallization experiments have been carried out to evaluatethe effect of solvent composition on crystal habit at constantsupersaturation. The solubility of benzoic acid inethanol-water mixtures at the working temperatures has beendetermined. Electro-zone sensing determinations and microscopicmeasurements are used to characterize the final crystallineproduct. It has been found that the shape of the benzoic acidcrystals grown from ethanol-water solutions ranges from needlesto platelets. Platy particles possess a predominant basal plane(001), bound by (010) and (100) faces, while needles aredeveloped along the b-axis. Long needle-shaped particles havebeen produced at low initial bulk concentration and highethanol concentration in the feed. Small platelets are obtainedat high initial bulk concentrations and high waterconcentration in the feed. The effect of solvent composition on the growth rate hasbeen evaluated at constant supersaturation. Seed crystals arecharacterized by image analysis measurement both before andafter each experiment. Length and width dimensions have beenmeasured on the particle silhouette. The growth rate, thesolid-liquid interfacial energy and the surface entropy factorfor the (010) faces (length dimension) and (100) faces (widthdimension) have been estimated. The interfacial energy andsurface entropy factor decreases in the direction of increasingethanol concentration due to increasing solubility. The results suggest that at low ethanol concentration(xEtOH&lt;60%) growth proceeds by screw dislocation mechanism,and adsorption of ethanol molecules may reduce the growth rate.As the ethanol concentration increases above a critical value(xEtOH ≥60%), the growth mechanism shifts to surfacenucleation and the growth rate increases with increasingethanol concentration. It has been suggested that the observedeffect of the solvent composition on crystal habit is theresult of two conflicting effects here referred as the kineticand interfacial energy effects. High interactions of the pairethanol-benzoic acid seem to be responsible of the growthretardation (kinetic effect) exerted by the solvent. On theother hand, increased ethanol concentration leads to reduceinterfacial energy and increasing surface nucleation whichmight contribute to enhance growth kinetics. <b>Keywords:</b>drowning-out crystallisation, solventcomposition, benzoic acid, solubility, crystal growth,interfacial energy, surface entropy factor, growth mechanism,crystal shape distribution.

The objective of this study is to synthesize nanomaterials by mixing molten salt (alkali nitrate salt eutectics) with inorganic nanoparticles. The thermo-physical properties of the synthesized nanomaterials were characterized experimentally. Experimental results allude to the existence of a distinct compressed phase even for the solid phase (i.e., in the nanocomposite samples). For example, the specific heat capacity of the nanocomposites was observed to be enhanced after melting and re-solidification - immediately after their synthesis; than those of the nanocomposites that were not subjected to melting and re-solidification. This shows that melting and re-solidification induced molecular reordering (i.e., formation of a compressed phase on the nanoparticle surface) even in the solid phase - leading to enhancement in the specific heat capacity. Numerical models (using analytical and computational approaches) were developed to simulate the fundamental transport mechanisms and the energy storage mechanisms responsible for the observed enhancements in the thermo-physical properties. In this study, a simple analytical model was proposed for predicting the specific heat capacity of nanoparticle suspensions in a solvent. The model explores the effect of the compressed phase – that is induced from the solvent molecules - at the interface with individual nanoparticles in the mixture. The results from the numerical simulations indicate that depending on the properties and morphology of the compressed phase – it can cause significant enhancement in the specific heat capacity of nanofluids and nanocomposites. The interfacial thermal resistance (also known as Kapitza resistance, or “Rk”) between a nanoparticle and the surrounding solvent molecules (for these molten salt based nanomaterials) is estimated using Molecular Dynamics (MD) simulations. This exercise is relevant for the design optimization of nanomaterials (nanoparticle size, shape, material, concentration, etc.). The design trade-off is between maximizing the thermal conductivity of the nanomaterial (which typically occurs for nanoparticle size varying between ~ 20-30nm) and maximizing the specific heat capacity (which typically occurs for nanoparticle size less than 5nm), while simultaneously minimizing the viscosity of the nanofluid. The specific heat capacity of nitrate salt-based nanomaterials was measured both for the nanocomposites (solid phase) and nanofluids (liquid phase). The neat salt sample was composed of a mixture of KNO3: NaNO3 (60:40 molar ratio). The enhancement of specific heat capacity of the nanomaterials obtained from the salt samples was found to be very sensitive to minor variations in the synthesis protocol. The measurements for the variation of the specific heat capacity with the mass concentration of nanoparticles were compared to the predictions from the analytical model. Materials characterization was performed using electron microscopy techniques (SEM and TEM). The rheological behavior of nanofluids can be non-Newtonian (e.g., shear thinning) even at very low mass concentrations of nanoparticles, while (in contrast) the pure undoped (neat) molten salt may be a Newtonian fluid. Such viscosity enhancements and change in rheological properties of nanofluids can be detrimental to the operational efficiencies for thermal management as well as energy storage applications (which can effectively lead to higher costs for energy conversion). Hence, the rheological behavior of the nanofluid samples was measured experimentally and compared to that of the neat solvent (pure molten salt eutectic). The viscosity measurements were performed for the nitrate based molten salt samples as a function of temperature, shear rate and the mass concentration of the nanoparticles. The experimental measurements for the rheological behavior were compared with analytical models proposed in the literature. The results from the analytical and computational investigations as well as the experimental measurements performed in this proposed study – were used to formulate the design rules for maximizing the enhancement in the thermo-physical properties (particularly the specific heat capacity) of various molten salt based inorganic nanomaterials. The results from these studies are summarized and the future directions are identified as a conclusion from this study.

Le circuit primaire d'une centrale nucléaire est composé d'un ensemble d'éléments très différents (cuve, coeur, réseau de conduite ...). A chacun de ces éléments correspond actuellement un ou plusieurs codes de calcul spécifiques basés sur des systèmes d'équations aux dérivées partielles spécifiques. Afin de permettre la simulation des écoulements diphasiques dans l'ensemble du circuit primaire, il faut envisager de coupler ces différents codes. L'approche proposée dans ce travail de thèse est de coupler les codes grâce à un échange d'information interfaciale instationnaire. Des flux numériques sont calculés au niveau des interfaces de couplage et servent de conditions aux limites à chacun des codes. Les méthodes permettant le calcul des flux de couplage sont dérivées du formalisme de Greenberg-Leroux proposé dans le cadre du décentrement des termes sources des systèmes hyperboliques non-homogènes stationnaires, et font intervenir un modèle d'interface. Trois cas de couplage ont été examinés : (i) le couplage du système des équations d'Euler en dimension un et deux ; (ii) le couplage de deux modèles diphasiques homogènes distincts ; (iii) le couplage d'un modèle homogène à quatre équations et du modèle bi-fluide standard.