The successful production of a wide range of polymer latex products relies on the ability to control the rates of particle nucleation, growth and coagulation in order to maintain control over the particle size distribution (PSD). The development of advanced population balance models (PBMs) has simplified this task at the laboratory scale, but commercialization remains challenging as it is difficult to maintain control over the composition (i.e. spatial distributions of reactant concentration) of larger reactors. The objective of this thesis is to develop and test a combined Computational Fluid Dynamics (CFD) -PBM hybrid modeling framework. This hybrid modeling framework can be used to study the impact of changes in process scale on product quality, as measured by the PSD. The modeling framework developed herein differs from previously-published frameworks in that it uses information computed from species tracking simulations to divide the reactor into a series of interconnected zones, thereby ensuring the reactor is zoned based on a mixing metric. Subsequently, an emulsion polymerization model is solved on this relatively course grid in order to determine the time evolution of the PSD. Examination of shear rate profiles generated using CFD simulation (at varying reactor scales) suggests that, dependent on conditions, mechanically-induced coagulation cannot be neglected at either the laboratory or the commercial scale. However, the coagulation models that are formulated to measure the contributions of both types of coagulation simultaneously are either computationally expensive or inaccurate. For this reason the decision was made to utilize a DLVO-coagulation model in the framework. The second part of the thesis focused on modeling the controlled coagulation of high solids content latexes. POLY3D, a CFD code designed to model the flow of non-Newtonian fluids, was modified to communicate directly with a multi-compartment PBM. The hybrid framework was shown to be well-suited for modeling the controlled coagulation of high solid content latexes in the laminar regime. It was found that changing the size of the reactor affected the latex PSD obtained at the end of the process. In the third part of the thesis, the framework was adapted to work with Fluent, a commercial CFD code, in order to investigate the scale-up of a styrene emulsion polymerization reaction under isothermal conditions. The simulation results indicated that the ability to maintain good control of the PSD was inversely related to the reactor blend time. While the framework must be adapted further in order to model a wider range of polymerization processes, the value of the framework, in obtaining information that would otherwise be unavailable, was demonstrated. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2012-05-01 07:09:08.362

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Thesis (Ph.D. (Pharmacy))--North-West University, Potchefstroom Campus, 2008.

Thesis (Ph.D. (Pharmacy))--North-West University, Potchefstroom Campus, 2008.

Optical biosensors are desired for the monitoring of various biochemical markers, which are relevant indicators in the treatment and diagnosis of diseases. Specifically, luminescence sensors are favorable for optical interrogation since they are highly sensitive to analyte changes and may be implemented in lifetime or intensity-based systems. In order to develop particle-based fluorescent sensors, poly(2-hydroxyethylmethacrylate) (HEMA) microspheres have been fabricated via membrane emulsification and characterized to evaluate the emulsion method and the overall process of tailoring properties to synthesize spheres of specific mean sizes. A pH-sensitive indicator seminaphthorhodafluors-4F 5-(and-6)-carboxylic acid (SNARF) was immobilized within the microspheres, and resulting sensor particles were exposed to various pH buffers to obtain a pH calibration curve based on intensity measurements. PolyHEMA microparticles were fabricated in a systematic study with measured mean sizes ranging from 8-21 um. Optical and scanning electron microscopy images revealed the formation of spherical, porous particles, which were additionally stabilized with polymer coatings. The lowest coefficient of variation value achieved was 50%, indicating the inability to produce monodisperse particles due to the dispersity of pore sizes in the membrane. SNARF was immobilized within the polyHEMA spheres, and fluorescence was observed when exposing the sensors to different pH buffers on a fluorescence microscope. Ratiometric intensity measurements for the sensor particles were obtained on a spectrofluorometer while flowing pH buffers over the immobilized spheres in a reaction chamber. The peak intensity ratio of the microparticle sensors exhibited a change in 0.9 units when decreasing the pH from 8.4 to 5.5. In the future, these pH sensing particles may be implanted alongside glucose sensing materials in order to provide valuable pH information in understanding the immune response to specific biomaterials and sensing components.

Heterogeneous catalytic reactions that involve immiscible liquid-phase reactants are challenging to conduct due to limitations associated with mass transport. Nevertheless, there are numerous reactions such as esterification, transesterification, etherification, and hydrolysis where two immiscible liquid reactants (such as polar and non-polar liquids) need to be brought into contact with a catalyst. With the intention of alleviating mass transport issues associated with such systems but affording the ability to separate the catalyst once the reaction is complete, the overall goal of this study is geared toward developing a catalyst that has emulsification properties as well as the ability to phase-transfer (from liquid-phase to solid-phase) while the reaction is ongoing and evaluating the effectiveness of such a catalytic process in a practical reaction. To elucidate this concept, the transesterification reaction was selected. Metal-alkoxides that possess acidic and basic properties (to catalyze the reaction), amphiphilic properties (to stabilize the alcohol/oil emulsion) and that can undergo condensation polymerization when heated (to separate as a solid subsequent to the completion of the reaction) were used to test the concept. Studies included elucidating the effect of metal sites and alkoxide sites and their concentration effects on transesterification reaction, effect of various metal alkoxide groups on the phase stability of the reactant system, and kinetic effects of the reaction system. The studies revealed that several transition-metal alkoxides, especially, titanium and yttrium based, responded positively to this reaction system. These alkoxides were able to be added to the reaction medium in liquid phase and were able to stabilize the alcohol/oil system. The alkoxides were selective to the transesterification reaction giving a range of ester yields (depending on the catalyst used). It was also observed that transition-metal alkoxides were able to be recovered in the form of their polymerized counterparts as a result of condensation polymerization subsequent to completion of the transesterification reaction.

Lycopene has recently received interest as an antioxidant in human tissues. These same antioxidant properties present challenges in preventing oxidative degradation within food products. In this research, degradation of lycopene in model emulsion systems was examined to better understand the chemical stability of this potential functional food ingredient.

Emulsions and foams are thermodynamically unstable dispersions that will eventually succumb to coalescence, leading to phase separation. However the kinetic stability of emulsions and foams can vary from transiently stable systems with lifetimes of seconds to indefinitely stable systems with lifetimes of many years. Understanding and controlling emulsion and foam stability is fundamental to their widespread application in consumer products and industrial processes. Designed stimuliresponsive peptide surfactants that allow the stability of emulsions and foams to be controlled by changes in solution conditions have recently been developed at the University of Queensland. The research objective of this thesis was to establish the mechanism by which these switchable biosurfactants control emulsion and foam stability and hence contribute design rules for future generations of peptide surfactants. In particular, research focused on the control of emulsion coalescence kinetics and the fundamental insights that these peptide-based emulsions provide into the coalescence phenomena. It was proposed that these switchable peptide surfactants allow the mechanical strength of the viscoelastic surfactant layer to be decoupled from other contributions to emulsion stability. It was found that the established Derjaguin– Landau–Vervey–Overbeek (DLVO) theory, which is frequently used as the basis for predicting emulsion stability, was not able to describe the stability switching observed in the peptide-based emulsions. Different designs of peptide surfactant were used to demonstrate that the kinetics of emulsion coalescence could be shifted by changing the interfacial elasticity, clearly illustrating the critical role of the surfactant layer’s mechanical properties in the coalescence mechanism. Where the peptide-surfactant-based emulsions enabled triggering a rapid transition to coalescence from a flocculation stable system it was shown that both the electrostatic repulsion (flocculation barrier) and the interfacial elasticity (coalescence barrier) were switched. This work made use of a number of experimental techniques to study the coalescence mechanism, including the observation of droplet interactions in microfluidic channels. The switchable peptide surfactants were shown to enable triggered coalescence in droplet based microfluidics, something that had hereto with proved an intractable challenge for surfactant containing oil-in-water systems. Having established the importance of the mechanical properties of the adsorbed peptide layer in enabling control over coalescence kinetics, it was of interest to study the effect of adding other surfactant species. Mixed surfactant systems are likely to be encountered in industrial applications or commercial products. The peptide surfactant AM1 was mixed with the common anionic surfactant sodium dodecyl sulfate (SDS) and synergistic behaviour was identified, including enhanced interfacial adsorption and reversible association of structures in the bulk solution. Furthermore the interfacial layers formed by AM1-SDS retained the switchable mechanical behaviour despite considerable increases in the absolute mechanical strength.

Abstract This work investigates the kinetics of the emulsion polymerization of vinyl acetate. Several aspects of this system have been clarified, including the induced decomposition of persulfate, retardation by oxygen and entry by, and analysis of, the aqueous phase oligomeric radicals. It has been shown that the retardation period observed in the emulsion polymerization of VAc can be explained by the effect of traces of oxygen (< 10-6 M) on the entry efficiency of the initiator-derived aqueous-phase oligomeric radicals. Comparison of rates of polymerization in V and persulfate -initiated polymerizations together with electrospray mass spectrometry of aqueous phase oligomers, has shown that the mechanism for the induced decomposition of persulfate by vinyl acetate is chain transfer to initiator from aqueous-phase oligomeric radicals. A value has been determined for the rate coefficient for transfer to initiator, by fitting literature data to a model based on this mechanism. The reported independence of the rate of polymerization from the monomer concentration in the emulsion polymerization of vinyl acetate has been investigated. Possible explanations for this behaviour have been proposed and tested in this work, by measuring radical-loss rates directly with y-relaxation techniques. Although the Y relaxations were found to be affected by experimental artefacts, it has been demonstrated that rapid exit is not responsible for the high radical-loss rates in this system. The major artefact identified in the y relaxations was the significant effect of relatively small exotherms on relaxation behaviour, Methodologies were developed for correcting affected data and for avoiding exotherms under certain conditions. Arrhenius parameters were determined for the rate coefficient for chain transfer to monomer using the In^M method, which utilises the whole MWD. This section of the work is incomplete, for reasons detailed in chapter 5. However, as a preliminary indication it was found that the frequency factor was 106.38 M-1 s-1 and the activation energy was 38.8 kJ mol-1.