This thesis is concerned with the derivation, development, and validation of a model for the dynamic behaviour of gas bubbles in molten instant coffee, in response to changes in pressure and temperature. Initially, the material properties of molten instant coffee were investigated. The primary technique used was capillary rheometry, as the viscous behaviour of molten instant coffee is a major contributor to the behaviour of bubbles within the fluid. The experimental technique was supplemented by analytical and computational modelling of the pressure losses in the system, to improve data processing accuracy. Additional thermal and mechanical tests were performed to obtain as much of the necessary material information as possible for the system. The modelling of bubble behaviour was performed using a combination of analytical and computational methods. The relationship between the pressure driving force for bubble growth or shrinkage and the rate of change of bubble size was derived analytically for a number of common generalised Newtonian fluid models. Heat and mass transfer between the bubble and the surrounding fluid was calculated using a finite difference approximation of the governing partial differential equations. The model was written in MATLAB and initial validation was carried out by comparison with existing models for bubble dynamics. Experimental observations of bubble dynamics in flows of molten instant coffee were recorded and used for an extended validation of the model. Bubbles were exposed to step changes in pressure and oscillatory pressure profiles at a range of temperatures, and the observations of 130 individual bubbles were used to validate the model using the same material parameters for each. A final case study in using the bubble model to predict the bubble size and pressure distribution created by an extrusion process is presented as an example of the use of the model, and highlights the additional information about a process that is required to effectively use the model.

Resumo: A Nanotecnologia é hoje um dos principais focos das atividades de pesquisa, desenvolvimento e inovação em todos os países industrializados. O uso da pele como alternativa para a administração sistêmica de fármacos constitui motivação e definição no investimento de novas pesquisas. Assim, veicular um fármaco pela via transdérmica apresenta inúmeras vantagens em relação a outras vias de administração de agentes terapêuticos. Muita atenção tem sido dada aos sistemas micro e nanoestruturados de tensoativos, por sua capacidade em aumentar a eficácia terapêutica de fármacos, permitindo a redução da dose administrada e minimizando os efeitos colaterais potenciais dos fármacos. A avaliação reológica e do comportamento fluidodinâmico de nanoemulsões tem sido pouco descrita na literatura, contudo, esta propriedade reveste-se de especial importância no seu desenvolvimento, pois pode representar uma limitação na administração de fármacos. Este trabalho pretende servir de fomento aos estudos de comportamento de nanofluidos, visando aplicações nessa interface de ciências farmacêuticas e engenharia / Abstract: Nanotechnology is today one of the main focus of the activities of research, development and innovation in all industrialised countries. The use of the skin as an alternative to the systemic administration of drugs is motivation and definition of the investment of new researches. Thus, vehicular a drug by Transdermal administration offer numerous advantages in relation to other routes of administration of therapeutic agents. Much attention has been given to micro and nanostructure systems of tensoactives, by its capacity in increasing the therapeutic efficacy of drugs, allowing the reduction in the dose administered and minimizing the potential side effects of drugs. The evaluation rheological and behavior hydrodynamics of nanoemulsions has been little described in the literature, however, this property is of particular importance in their development, because it may represent a limitation in the administration of drugs. This work intends to serve to promote studies behavior nanofluidos, aiming at applications interface of pharmaceutical sciences and engineering / Orientador: Luiz Roberto Carrocci / Coorientador: Luiz Fernando Costa Nascimento / Banca: Petrônio Masanobu Tanisho / Banca: Daniela Camargo Vernilli / Mestre

Thesis submitted in fulfilment of the requirements for the degree Doctor of Technology: Chemical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2014 / This study investigated water-in-oil (W/O) super-concentrated emulsions used as pumpable explosives. The aqueous phase of the emulsions is a supersaturated nitrate salt solution (at room temperature), with a volume fraction of approximately 0.9. Instability of such emulsions arises either from crystallization of the dispersed phase in the system during ageing or under high shear conditions. Here, we report an alternative approach to stabilize this highly concentrated W/O emulsion by adding colloidal particles in combination with short amphiphilic molecules. Thus, the primary goal of this research concerned a phenomenological study of the dependence of surfactant-to-particle ratio as well as the particle hydrophobicity index on stability under high shear in the emulsification process, rheological properties and stability against initiation of crystallization of an internal phase both with ageing and under high shear with a view to optimize the time to the start of crystallization of the emulsion both with ageing and under high shear; to elucidate the mechanism of initiation of crystallization of an internal phase (homogeneous or heterogeneous) and shed light in the stabilization mechanism of the emulsion; to determine how the emulsion formulation content affect pumping characteristics as measured by characteristic rheological parameters. A series of five fumed silica nanoparticles, each with a different hydrophobicity index (HI) in the range of 0.60 – 3, were used in the form of single types of particles as well as binary mixtures. These particles were combined with a low molecular weight conventional surfactant, Sorbitan MonoOleate (SMO), into the oil phase prior to emulsification. It has been found that regardless of the particle hydrophobicity, fumed nanosilica alone cannot form highly concentrated W/O emulsion up to 90 vol%. Moreover, Pickering emulsions are unstable under shear conditions and thus it is difficult to make highly concentrated W/O pumpable emulsion explosives using only fumed nanosilica. The correlation between the refinement time and SMO-to-particle ratio showed a deflection point/transitional point in the stabilization mechanism. Below the transitional point the silica content dominates over SMO. Conversely, above the transitional point the particles have little effect and the SMO dominates. A thermodynamic consideration revealed that in this region only SMO is likely to adsorb at the W/O interface and controls the emulsifying process. As with refinement time, the correlation between the shear modulus and SMO/particle ratio shows a deflection /transitional point which, as before, mark the transition point between regions of particle or SMO domination. Interestingly, it was found that for each HI, the initiation of crystallization is the most delayed, both on shelf life and under high shear, when the emulsion is prepared with an SMO-to-particle ratio equaling exactly the value at this transitional point. Moreover, the research demonstrated that a drastic change in mechanism of initiation of crystallization of the dispersed droplets occurs at the transitional point. Homogeneous nucleation within the droplets is the dominating mechanism of initiation of crystallization of an internal phase for SMO/particle ratios below and at the transitional point. In this case, the relationship between the zero modulus of particle dispersions in oil and the SMO-to-particle ratio demonstrated that the most stable emulsions are formed from the most unstable dispersions, indicating that less repulsion between particles is required to delay the onset of crystallization. This was further corroborated by the linear correlation between the time to the onset of crystallization and the shear modulus of the emulsion. On the contrary, it was found that for SMO/particle ratios above the critical point, heterogeneous nucleation catalyzed at the surface of droplets is the dominating mechanism of initiation of crystallization of nitrate salts in the super-cooled droplets This was found to be consistent with SMO-only system. That is the change in the mechanism of initiation of crystallization originates from a drastic change in the emulsion structure due to excess surfactant was highlighted by the drastic change in the linear correlation between the time to the start of crystallization and the strength of the emulsion structure as measured by the shear modulus. The optimum time to the start of crystallization (onset of crystallization associated with optimum SMO-to-particle ratio) is sensitive to the particle HI; increasing with increase of particle HI. A general correlation between the particle HI and optimum time to the onset of crystallization has been identified and formulated for the whole family of single types and mixtures of fumed nanosilica used in this study.

Thesis (DTech (Chemical Engineering))--Cape Peninsula University of Technology, 2005. / The subject of this study is highly concentrated emulsion explosive (HCEE). These emulsions are dispersions of an aqueous phase (up to 90 v-%) in an oil phase. The dispersed droplets consist of an aqueous solution of nitrate salts, which is supersaturated at room temperature, comprising less than 20% of water by mass. Compounds of this kind are thermodynamically unstable and their instability is related to the coarsening of emulsion (coalescence) and phase transition (crystallization) of dispersed phase. However it is demonstrated that the dominating mechanism is slow crystallization inside the super-cooled droplets. The main goal of this thesis is a phenomenological study of the dependence of structural parameters, such as droplet size and volume fraction, as well as the ageing processes, on the rheological properties of these emulsions. The results of the measurements include the flow and viscoelastic properties of the materials. The rheological parameters are correlated with the kinetics of structural changes during ageing, as a function of emulsion formulation. The emulsions under study are non-Newtonian liquids. Experiments in shear rate sweep mode demonstrate that the upward and downward branches of the flow curves coincide above some specific shear rate value. The upward experiments show the existence of a low shear Newtonian asymptote, while the effect of yielding is observed in the downward curve. Wall slip is investigated and shown to be negligible.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2009. / The purpose of emulsification process is to create numerous small droplets from a large and homogenous oil phase. The emulsion used for this study is new thermodynamically unstable multi-component water-in-oil (w/o) explosive type with an internal phase ratio of approximately 94% (wt), i.e. far beyond the close packing limit of spherical droplets of 74%. However, little work has been done for this system, pertaining to the literature explaining what physical phenomena plays a major role in the process of drop formation during highly concentrated emulsion (HGE) manufacturing. This thesis is devoted to develop an understanding of what parameters control drop formation and rupture during processing of highly concentrated emulsions. The material used for the study consisted of three Pibsa derivatives (MEA, IMIDE and UREA), one mixture (MEA/SMO, 10:1) and SMO. Two concentrations were used namely 8% and 14% and the two fuel phase material were Mosspar-H and Shell sol. The Pibsa IMIDE was carried out in both oil phases. To carry out the study, the Hobart N50 mixer coupled with a power and harmonic analyser to record power as a function of time was used to manufacture all samples for the study.

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A brief review is made of the rheology of suspensions in general and cement slurries in particular. The factors influencing the flow behaviour of these systems are discussed. It is pointed out that the rheological properties of cement slurries can not be determined by theory alone from the original constituents, and experimental tests combined with empirical formulae are needed. The co-axial cylinder viscometer was used to characterise the rheological behaviour of the cement slurry used in this investigation, the slurry being made highly thixotropic by the use of additives, It is shown that no single flow model, however complex, can correctly fully describe the flow behaviour of such materials. The cement slurry used in this research programme had a structure which changed continuously with time and, when pumped through a pipe, formed a high water content slip layer on the pipe surface. An accurate theoretical solution for this type of pipe flow is lacking in the literature. A new method to predict the pressure gradient of such suspensions flowing in pipes is proposed and the technique was tested using a small pumping line and also with data extracted from the literature. The shear vane test, commonly used to measure shear strength of soils, was developed to measure gel strength of the cement slurry used in this investigation. It is shown that the gel strength measured with this technique is of considerable benefit when assessing the real material behaviour.

Taken as an engineering material, mozzarella cheese can be considered as a complex food system that has dynamic structure and complex flowproperties. Food scientists have been actively developing methods to characterize mozzarella cheese rheologically, but most of these methods are empirical in nature. In the past decades, there has been a paradigm shift towards the utilization of well-developed rheological methods which have been widely applied in the study of commercial synthetic polymers. In this work, the rheology of mozzarella cheese was studied using well-developed rheological techniques. Utilizing various rheometers, the linear and non-linear rheology of mozzarella cheese was examined. General practical properties of mozzarella cheese such as meltability, flowability and stretchability were extracted from these results. Capillary flow and rolling experiments were also performed to determine their suitability as innovative post-production processing techniques for mozzarella cheese. Finally, a comparative study on the effect of frozen storage on the rheology of three different brands of mozzarella cheese was performed. In general, it was found that mozzarella cheese can be classified as a pseudoplastic (shear thinning) semi-solid material possessing a yield stress at room temperature. Upon heating, the yield stress gradually diminishes and it can be considered as a viscoelastic fluid. The results obtained from the various rheometers indicate that the yield stress, duration of experiment, sample geometry and temperature greatly affect the consistency of the results. It was also shown that extrusion can be used as a processing technique for mozzarella cheese above a certain temperature where the cheese is in a melt state. Rolling was also found to be a potentially feasible processing method. Finally, in terms of the effect of frozen storage, in general, the dynamic moduli decrease with the period of storage due to the freezing of the proteins in the cheese. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Rheological and processing behavior of a number of linear low-density polyethylene(LLDPE)/low-density polyethylene (LDPE) blends was studied with emphasis on the effects of long chain branching. First, a linear low-density polyethylene (LL3001.32) was blended with four LDPE's having distinctly different molecular weights. At high LDPE weight fractions, DSC melting thermograms have shown three different polymer phases; two for the pure components and a third melting peak of co-crystals. Different rheological techniques were used to check the thermo rheological behavior of all blends in the melt state and the effect of long chain branching. It was found that all blends are miscible in the melt state at small LDPE concentrations. The elongational behavior of the blends was studied using a uniaxial extensional rheometer, SER. The blends exhibit strain hardening behavior at high rates of deformation even at LDPE concentrations as low as 1%, which suggests the strong effect of branching added by the LDPE component. On the other hand, shear rheology was found to be insensitive to detect addition of small levels of LDPE up to lwt%. The second set of blends prepared and studied consisted of two Ziegler-Natta LLDPE's (LL3001.32 and Dowlex2045G) and two metallocene LLDPE's(AffinityPL1840 and Exact 3128) blended with a single LDPE. In DSC melting thermograms, it was observed that blends with metallocence LLDPE's exhibit a single melting peak at all compositions; whereas the Ziegler-Natta blends exhibit three melting peaks at certain compositions. It was found also that the metallocene LLDPE's are miscible with the LDPE at all concentrations. On the other hand, the Ziegler-Natta LLDPE's were found to be miscible with LDPE only at small LDPE concentrations. The processing behavior of all blends with emphasis on the effects of long chain branches was also studied in capillary extrusion. The critical shear stresses for the onset of sharkskin and gross melt fracture are slightly delayed with the addition of LDPE into LLDPE. Furthermore, the amplitude of the oscillations in the stick-slip flow regime, known as oscillating melt fracture, were found to scale with the weight fraction of LDPE. Amounts as low as 1 wt% LDPE have a significant effect on the amplitude of pressure oscillations. These effects are clearly due to the presence of LCB. It is suggested that the magnitude of oscillations in the oscillating melt fracture flow regime can be used as a method capable to detect low levels of LCB. Finally, the sharkskin and stick-slip polymer extrusion instabilities of a linear low-density polyethylene were studied as a function of the type of die geometry. The critical wall shear stress for the onset of flow instabilities, the pressure and flow rate oscillations, and the effects of geometry and operating conditions on the instabilities are presented for a LLDPE. It was found that sharkskin and stick-slip instabilities were present in the capillary and slit extrusion. However, stick-slip and sharkskin in annular extrusion are absent at high ratios of the inside to outside diameter of the annular die. This observation also explains the absence of these instabilities in polymer processing operations such as film blowing. These phenomena are explained in terms of the surface to volume ratio of the extrudates. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate