Complex interfaces stabilized with materials including surfactants, polymers, and particles have dilatational properties that are important in processing emulsions and foams. Dilatational rheology is difficult to measure on interfaces due to the coupling of dilatation and shear inherent in common measurement apparatuses. Compounding the problem is the lack of control over complex interface formation in emulsification, which can obscure relationships between interfacial rheology and bulk emulsion properties. This thesis provides tools to measure dilatational properties of interfaces and generate interfaces with controlled surface coverage. A small amplitude analysis of dilatational rheology on capillary pressure tensiometers is used to develop a method for separating intrinsic rheology from surface tension effects. This analysis is applied in dilatational measurements of insoluble interfaces at the microscale, and good agreement is observed between the microscale measurements and Langmuir trough measurements. The second half of the thesis focuses on the controlled generation of particle-stabilized interfaces. A two-lobed shape transition is observed for confined bubbles traveling in a surface active particle suspension, and a model is developed to predict the particle surface coverage on the bubble interface. This model is then applied to generate monodisperse bubbles with uniform nonspherical bubbles due to particle jamming at the interface. The tools developed in this thesis are crucial to future development of relationships between the dilatational rheology of interfaces and the bulk properties of emulsions and foams.

This thesis is concerned with the performance and measurement uncertainty of wire-mesh sensors in different air-water flow regimes in horizontal pipes. It also presents measurements of void fraction and interfacial velocity in such flows. It was found that the interfacial velocity measurements of the wire-mesh sensors were in good agreement with those taken with a high-speed camera and estimates of the uncertainties of these measurements are presented. Drift-flux models were fitted to the measurements and it was found that the parameters of these models were not only sensitive to the flow regime, but also to the liquid superficial velocity.

Certain strains of hydrophobic bacteria are known to play critical roles in petroleum-related applications. The aim of this study was to investigate how hydrophobic bacteria in their stationary phase could adsorb onto the hexadecane-water interface and alter its mechanical properties. The two strains of bacteria used in forming the interfacial films were Acinetobacter venetianus RAG-1 (a Gram-negative bacterium) and Rhodococcus erythropolis 20S-E1-c (Gram-positive). Experiments at two different length scales (millimetre and micrometre) were conducted and the results were compared. In addition, a simple flow experiment was designed in a constricted channel and the results were related to the intrinsic mechanical properties of bacteria-adsorbed films. On the millimetre scale, using the pendant drop technique, the film interfacial tension was monitored as the surface area was made to undergo changes. Under static conditions, both types of bacteria showed no significant effect on the interfacial tension. When subjected to transient excitations, the two bacterial films exhibited qualitatively similar, yet quantitative distinct rheological properties (including film elasticities and relaxation times). Under continuous reduction of surface area, the RAG-1 system showed a “paper-like” interface, while the interface of the 20S-E1-c system was “soap film-like.” These macroscopic observations could be explained by the surface ultrastructures of the two cell strains. On the micrometre scale, using the micropipette technique, colloidal stability of the bacteria-coated oil droplets was examined through direct-contact experiments. Both types of bacteria were seen to function as effective stabilizers. In addition, the adsorbed bacteria also interacted with one another at the interface, giving rise to higher order 2-D rheological properties. A technique of directly probing the mechanical properties of the emulsion drop surfaces revealed that (a) the films behaved as purely elastic sheets, and (b) with a reduction in cell concentration in the aqueous phase, less oil was emulsified, but the elastic moduli of the adsorbed films remained unchanged. These results are in contrast to the above millimetre-scale study. Therefore the rheological properties of these bacteria-adsorbed films appear to be length scale-dependent. An oil displacement experiment was designed to investigate the flow behaviour of micron-scale emulsion drops in a constricted channel. The qualitative results can be correlated with the interfacial rheological properties and may have valuable relevance to the study of multiphase flow through constricted channels in porous rocks (e.g. in MEOR operations). / Chemical Engineering

A diffuse-interface finite-element method has been applied to simulate the flow of two-component rheologically complex fluids. It treats the interfaces as having a finite thickness with a phase-field parameter varying continuously from one phase to the other. Adaptive meshing is applied to produce fine grid near the interface and coarse mesh in the bulk. It leads to accurate resolution of the interface at modest computational costs. An advantage of this method is that topological changes such as interfacial rupture and coalescence happen naturally under a short-range force resembling the van der Waals force. There is no need for manual intervention as in sharp-interface model to effect such event. Moreover, this energy-based formulation easily incorporates complex rheology as long as the free energy of the microstructures is known. The complex fluids considered in this thesis include viscoelastic fluids and nematic liquid crystals. Viscoelasticity is represented by the Oldroyd-B model, derived for a dilute polymer solution as linear elastic dumbbells suspended in a Newtonian solvent. The Leslie-Ericksen model is used for nematic liquid crystals，which features distortional elasticity and viscous anisotropy. The interfacial dynamics of such complex fluids are of both scientific and practical significance. The thesis describes seven computational studies of physically interesting problems. The numerical simulations of monodisperse drop formation in microfluidic devices have reproduced scenarios of jet breakup and drop formation observed in experiments. Parametric studies have shown dripping and jetting regimes for increasing flow rates, and elucidated the effects of flow and rheological parameters on the drop formation process and the final drop size. A simple liquid drop model is used to study the neutrophil, the most common type of white blood cell, transit in pulmonary capillaries. The cell size, viscosity and rheological properties are found to determine the transit time. A compound drop model is also employed to account for the cell nucleus. The other four cases concern drop and bubble dynamics in nematic liquid crystals, as determined by the coupling among interfacial anchoring, bulk elasticity and anisotropic viscosity. In particular, the simulations reproduce unusual bubble shapes seen in experiments, and predict self-assembly of microdroplets in nematic media.

Viscous fingering occurs when one fluid displaces another fluid of a greater viscosity in a porous medium or a Hele-Shaw cell. Linear stability analysis is used to predict methods of suppressing instability. Then, experiments in which nonlinear growth dominates pattern formation are analysed to explore the nonlinear impact of strategies of suppressing finger growth. Often, chemical treatment fluid is injected into oil reservoirs in order to prevent sand production. This treatment fluid is usually followed by water injection to clean up the well. We explore the potential for viscous instability of the interface between the treatment fluid and the water, and also the treatment fluid and the oil, as a function of the volume of treatment fluid and the injection rate and viscosity ratios of the different fluids. For a given volume of treatment fluid and a given injection rate, we find the optimal viscosity of the treatment fluid to minimise the viscous instability. In the case of axisymmetric injection, the stabilisation associated with the azimuthal stretching of modes leads to a further constraint on the optimisation of the viscosity. In the case of oil production, polymers may be added to the displacing water in order to reduce adverse viscosity gradients. We also explore the case in which these polymers have a time-dependent viscosity, for example through the slow release from encapsulant. We calculate the injection flow rate profile that minimises the final amplitude of instability in both rectilinear and axisymmetric geometries. In a development of the model, we repeat the calculation for a shear-thinning rheology. Finally, experiments are analysed in which the nonlinear growth of viscous fingers develops to test the influence of different injection profiles on the development of instability. Diffusion Limited Aggregation (DLA) simulations are performed for comparison. In all cases, the evolving pattern has a saturation distribution, with an inner zone in which the fingers are static and an outer zone in which the fingers advance and grow. In the very centre of the viscous fingering patterns, there is a small fully-saturated region. In the experiments, the mass distribution in the inner zone varies with radius as a power law which relates to the fractal dimension for the analogue DLA simulations. In the outer region the saturation decreases linearly with radius. The radius of the inner frozen zone is approximately 2/3 of the outer radius in the cases of DLA and -- after a period of evolution -- the viscous fingering experiments. This allows the radial extents of the inner and outer zones to be predicted. The ratio of each radius to the extent of the fully-saturated region is independent of the injection profile and corresponds to values for DLA.

La formation d’émulsions stables eau/huile lors des processus de récupération et de raffinage du pétrole peut impacter défavorablement l’efficacité de ces opérations. Bien que résines et asphaltènes soient généralement tenus pour responsables de la stabilité des émulsions, la composition exacte des molécules présentes à l’interface eau/huile est en réalité assez mal connue. L’identification de ces molécules et la connaissance de leur influence sur la propriété des interfaces est une étape nécessaire pour mieux prédire les problèmes de stabilité des émulsions dans l’industrie pétrolière. Cette thèse présente des résultats de caractérisation analytique par GPC-ICP-HRMS et FTMS du matériel interfacial (IM) extrait de quatre bruts différents et des espèces transférées dans la phase aqueuse lorsque ces bruts contactent l’eau, ainsi que des propriétés rhéologiques en cisaillement et en dilatation des interfaces eau/huile en présence de ces composés. Les bruts ont été choisis en raison de leur capacité à former des émulsions eau-dans-huile de stabilités différentes. Les mesures d’élasticité de cisaillement ont montré que la majorité des interfaces eau/huile étudiées formaient une structure élastique susceptible de fausser la mesure du module dilatationnel de Gibbs par la méthode d’analyse du profil de goutte. Néanmoins, nous montrons à l’aide de simulations numériques que le module apparent Eapp mesuré dans un tel cas est proche de la somme du module de Gibbs et du module de cisaillement (G) multiplié par 2 du réseau interfacial dès lors que G reste petit (G < 10 mN/m), ce qui est très souvent le cas puisque nous observons que le réseau interfacial formé se rompt lors des expériences de dilatation. Une équation phénoménologique a été développée permettant d’attribuer un temps de relaxation unique aux processus de relaxation qui ont lieu aux interfaces eau/huile, ce qui nous permet de classer les différents systèmes entre eux. Nous avons également étudié les IM extraits des bruts selon la technique chromatographique dite « wet silica method » récemment développée par Jarvis et al. (Energy Fuels, 2015). Les expériences de rhéologie interfaciale confirment que cette méthode permet d’extraire les composés les plus tensioactifs présents aux interfaces eau-brut. Les analyses chimiques montrent que les IM sont partiellement composés d’asphaltènes et suggèrent que les composés contenant du soufre jouent un rôle important dans la stabilité des émulsions. Enfin, nous avons trouvé que les composés hydrosolubles transférés du brut à l’eau ont un comportement bénéfique, dans le sens où leur présence rend les émulsions eau-dans-brut moins stables. L’analyse FTMS de ces composés montre qu’ils appartiennent aux classes d’hétéroatomes suivant : O2, O3, S1, OS et O2S2 et qu’une partie de ces composés appartient à la classe des asphaltènes. / Crude oil recovery and refining operations rely on high consumption water processes, which may induce the formation of stable water-in-oil emulsions. Although asphaltenes and resins are known to influence the stability of crude oil emulsions, much is still unknown about the real composition of the w/o interfacial layer. Therefore, identifying these molecules and understanding their impact on the w/o interfacial properties are key points for better predicting emulsion problems in the petroleum industry. This thesis presents results on water/oil (w/o) interface characterization using shear and dilatational interfacial rheology as well as results on molecular characterization (GPC-ICP-HRMS and FTMS) of the crude oil interfacial material (IM) and of the amphiphilic crude oil species, which are transferred to the aqueous phase during the emulsification process. Four crude oils forming w/o emulsions of different stability were used in this study. Shear interfacial rheology experiments showed that most of the studied w/o interfaces were capable of forming an elastic interfacial network exhibiting shear elasticity G. A non-null G value interferes on drop deformation and thus on drop shape analysis (DSA) results. Nevertheless, the dilatational elasticity modulus measured by DSA (Eapp) was found to be representative of the sum of the Gibbs modulus plus 2 times G, as long as G  10 mN/m. This condition is generally satisfied since the asphaltene network is broken during dilatational experiments. Consequently, Eapp gives a good approximation of the real Gibbs modulus of the interface. A new phenomenological equation was proposed to fit the dilatational Eapp experimental data, allowing the assignment of a unique characteristic time to describe the w/o interfacial relaxation process and thus sample comparison. The IM of the crude oils was extracted using the “wet silica method” recently developed by Jarvis et al. (Energy Fuels, 2015). Results showed that this method collects the most-surface active compounds that adsorb in the time frame of the extraction procedure. Successive extractions collected species that were larger and less concentrated in the crude oil, but with higher adsorption energies. Molecular characterization revealed that the IM was partially composed of asphaltene compounds, and suggested that sulfur-containing compounds may play a major role in emulsion stability. Lastly, the oil-to-water transferred species were proven to impact the w/o interfacial properties and emulsion stability. Interestingly, concentrating these water-soluble species led to more efficient crude oil dehydration. FTMS analysis of the transferred species revealed that part of the compounds belonged to O2, O3, S1, OS and O2S2 heteroatom classes, and some of them have an asphaltene-type of molecules classification.

Made available in DSpace on 2016-06-02T19:12:35Z (GMT). No. of bitstreams: 1 5913.pdf: 32719681 bytes, checksum: e0f7ffe5dcde1da6704dce9f4d62a8a7 (MD5) Previous issue date: 2014-07-01 / Financiadora de Estudos e Projetos / Hybrid filler reinforced thermoplastics composed with short glass fiber (GF) and different particulate fillers present special interest for engineering applications, as substantial reductions in mechanical anisotropy and molding warpage are expected from these systems as compared to the same characteristics inherent to binary composites with GF only. These improvements are achieved by the partial substitution of GF by particulate fillers and are attained at the cost of minor reductions in rigidity, strength and toughness properties of these ternary composites. However, when nanoscale fillers such as nanoclay (NC) are incorporated in GF-reinforced thermoplastics, the mechanical strength properties of these systems are severely affected, even at very low NC content. Thus in this work, using model GF-reinforced polypropylene (PP) composites with varying total and relative concentrations of GF and organophylic montmorillonite clay (O-MMT) along with maleated PP as compatibilizer were twin-screw extrusion compounded with three different mixing protocols, in order to identify the factors leading to the observed loss in mechanical strength properties. Using tensile, flexural, izod impact and dynamic-mechanical (DMTA) characterization tests and electron microscopy (SEM and TEM) elucidation of the fiber-matrix interface/interphase microstructure, it is concluded that the physical presence of NC particles at the interface contributes towards the reduction of interfacial interactions. As a consequence of low interfacial adhesion between the nanoclay and polymeric matrix, debonding of the particles and the PP during mechanical testing occurs, leading to crack growth that anticipates ternary hybrid composites failure in stress levels lesser compared with that of binary composites. These hypotheses were corroborated by SEM and TEM analyses. / Compósitos de termoplásticos com reforços híbridos de fibra de vidro (FV) curta e diversas cargas particuladas, tais como carbonato de cálcio, talco e esferas de vidro, apresentam características interessantes para aplicações de engenharia, já que se espera a redução substancial de problemas inerentes aos compósitos binários reforçados apenas com fibras, como são a anisotropia mecânica e o empenamento de peças moldadas por injeção. Tais aprimoramentos são alcançados mediante a substituição parcial da FV por carga particulada, porém, com leve decréscimo nas propriedades de resistência e tenacidade mecânica destes compósitos híbridos ternários. No entanto, quando reforços nanométricos, tais como nanoargilas, são incorporados em termoplásticos reforçados com FV, o efeito deletério nas propriedades de resistência e tenacidade é ainda mais crítico, inclusive em baixos teores do nanoreforço. Portanto, com o objetivo de identificar os fatores que levam à verificada queda de propriedades mecânicas, foram utilizados três protocolos diferentes de mistura para a preparação de compósitos híbridos ternários de polipropileno (iPP) reforçado com FV e nanoargila do tipo montmorilonita organofilizada (O-MMT), compatibilizados com PP funcionalizado com anidrido maleico, e variando a concentração total e relativa dos reforços. Para alcançar o objetivo traçado, foram usados ensaios de caracterização mecânica de curta duração (tração, flexão e impacto), termo-mecânica (HDT e DMTA) e elucidação microestrutural (MEV, MET). Concluiu-se que a presença física das partículas de O-MMT na proximidade da superfície das fibras tem efeito deletério na transferência de tensão cisalhante na interface fibra-polímero. Devido à relativamente baixa adesão interfacial existente entre a matriz e as partículas de nanoargila, durante a solicitação mecânica ocorre desacoplamento das partículas, dando lugar ao crescimento de trincas que antecipam a falha do compósito ternário em níveis de tensões menores que as sustentadas pelo compósito binário só com FV.

Made available in DSpace on 2014-06-12T23:13:44Z (GMT). No. of bitstreams: 2 arquivo750_1.pdf: 6128685 bytes, checksum: 2d8409ed6fea3b21f62cd544942da7e2 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Faculdade de Amparo à Ciência e Tecnologia do Estado de Pernambuco / O 4-amino-2-fenil, 6(p-fluor-fenil)-5-carbonitrila-pirimidina (APCP) é um novo derivado de pirimidina com baixa solubilidade em água e propriedade antiinflamatória. Neste trabalho, o comportamento interfacial do filme de 1,2-distearoil-sn-glicero-3-fosfoetanolamina-N-[poli(etileno glicol)2000], i.e., DSPE-PEG2000; 1,2-dipalmitoil-sn-glicero-3-fosfatidilcolina (DPPC) e de um novo derivado pirimidínico (APCP), foi avaliado e posteriormente comparados com o comportamento interfacial dos sistemas binários e ternários da mistura destas moléculas em diferentes frações molares. A isoterma de pressão de superfície-área (&#61520;-A) mostrou que as moléculas tanto de APCP quanto de DSPE-PEG2000 e DPPC formaram filmes estáveis na interface ar-água. O sistema binário (DPPC/DSPE-PEG2000) e ternário (DPPC/DSPE-PEG2000/APCP) apresentou miscibilidade entre os componentes. A inclusão do APCP na monocamada DPPC/DSPE-PEG2000 tornou o perfil mais expandido à medida que se aumenta a concentração de APCP. Além disso, a transição de mushroom para brush existente nas moléculas de PEG torna-se dificultada na presença do APCP ocorrendo apenas a 9mol% e em pressões de superfície acima de 10mN/m. Filmes de Langmuir-Blodgett contendo o sistema binário e ternário foram transferidos sobre substratos de mica para caracterização morfológica por microscopia de força atômica (AFM). Imagens de AFM demonstraram ausência de defeitos em ambos os sistemas e distribuição heterogênea da monocamada, com a amplitude entre os picos e vales na ordem de ~4 nm para o sistema binário e ~3 nm para o sistema ternário

This thesis is concerned with aspects of the surface and colloid chemistry of various microemulsion systems stabilised by pure nonionic surfactants and alcohol as well as mixtures of nonionic and anionic surfactants. Phase equilibria and interfacial characteristics of the systems are studied with a view to their potential usefulness for enhanced oil recovery, in which salinity and temperature are important parameters. The equilibrium microemulsion phases are scanned at different temperatures and salinities and thus interfacial boundaries can be determined and optimum salinity scans can be performed accurately using a modified spectrophotometer. Several analytical techniques (e.g., high performance liquid chromatography, gas chromatography, ion-exchange chromatography, mass spectrometry, viscometry, electrical conductivity, photon correlation spectroscopy, UV-spectrophotometry, thermogravimetric analysis, transmission electron microscopy, surface and interfacial tension techniques) have been used to characterise and understand the microchemistry of the microemulsion systems. Ultra-low interfacial tensions (>0.1 µN/m) can be achieved in the microemulsion systems. Surfactant transfer between phases, and phase inversion of micro emulsions are shown to occur around the condition which produces minimum interfacial tension. Adsorption of the surfactants from aqueous and nonaqueous solutions has been investigated and the results show that the extent of adsorption can be reduced significantly in the presence of alcohols (co-solvent). The extent of adsorption increases with increasing temperature and salinity; however, it decreases with an increase in the hydrophilic head group of the surfactant. Adsorption of nonionic surfactants on quartz from the nonaqueous solution (decane) is much greater than from aqueous solution. In microemulsion applications, droplet combustion of w/o microemulsions is also studied for different surfaces (i.e. silica, oxidised Fecralloy and catalyst coated Fecralloy) in the temperature range of 313-573K. Formaldehyde and acetaldehyde are formed as intermediate combustion products. Thus the microemulsion combustion can lead to new oxygenate products. The w/o microemulsion route is used to synthesize colloidal silica of controlled particle size and morphology. The particle size can be varied by changing the molar ratio of water to TEOS using a water pH of 10.5.

A diffuse-interface finite-element method has been applied to simulate the flow of two-component rheologically complex fluids. It treats the interfaces as having a finite thickness with a phase-field parameter varying continuously from one phase to the other. Adaptive meshing is applied to produce fine grid near the interface and coarse mesh in the bulk. It leads to accurate resolution of the interface at modest computational costs. An advantage of this method is that topological changes such as interfacial rupture and coalescence happen naturally under a short-range force resembling the van der Waals force. There is no need for manual intervention as in sharp-interface model to effect such event. Moreover, this energy-based formulation easily incorporates complex rheology as long as the free energy of the microstructures is known. The complex fluids considered in this thesis include viscoelastic fluids and nematic liquid crystals. Viscoelasticity is represented by the Oldroyd-B model, derived for a dilute polymer solution as linear elastic dumbbells suspended in a Newtonian solvent. The Leslie-Ericksen model is used for nematic liquid crystals，which features distortional elasticity and viscous anisotropy. The interfacial dynamics of such complex fluids are of both scientific and practical significance. The thesis describes seven computational studies of physically interesting problems. The numerical simulations of monodisperse drop formation in microfluidic devices have reproduced scenarios of jet breakup and drop formation observed in experiments. Parametric studies have shown dripping and jetting regimes for increasing flow rates, and elucidated the effects of flow and rheological parameters on the drop formation process and the final drop size. A simple liquid drop model is used to study the neutrophil, the most common type of white blood cell, transit in pulmonary capillaries. The cell size, viscosity and rheological properties are found to determine the transit time. A compound drop model is also employed to account for the cell nucleus. The other four cases concern drop and bubble dynamics in nematic liquid crystals, as determined by the coupling among interfacial anchoring, bulk elasticity and anisotropic viscosity. In particular, the simulations reproduce unusual bubble shapes seen in experiments, and predict self-assembly of microdroplets in nematic media. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate