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The study of the influence of surfactant molecules on foam behaviour is of considerable interest due to the importance of foam in numerous industrial processes. This thesis describes an investigation of the influence of molecular structure of simple non-ionic surfactant molecules on the Marangoni effect and foam behaviour. The aim of this study is to establish a clear scientific rationale for surfactant choice so that specific foam behaviour may be engineered. In order to achieve this outcome, the foam behaviour of simple non-ionic surfactants was investigated. / A simple model was developed to define the role of the Marangoni effect on foam behaviour. This model follows the surface tension changes on a single bubble, near the Plateau border and lamellar region, as the bubble rises from the liquid to the foam phase. This model requires a knowledge of the static and dynamic surface tensions of the surfactant solution as well as the bubble size distribution and retention time in both the liquid and foam phases. Using this model, the calculated surface tensions at the Plateau border and lamellar region for a bubble at the top of the foam were in good agreement with the trend of foamability with surfactant concentration. The Gibbs elasticity, which is the ability of surfactant to generate a surface tension difference on a bubble surface, was experimentally determined. With this model, parallel relationships were found between Gibbs elasticity and both the steady state and continuous flow foaming behaviour, after accounting for the non-equilibrium interfacial behaviour present in the foam. This study has emphasised the importance of the Marangoni effect in controlling foamability and shown how dynamic interfacial behaviour plays a major role. The prediction of foam behaviour from surfactant properties (e.g. Gibbs elasticity, static and dynamic surface tension) using the model developed in this study was illustrated / A preliminary study which relates the outcomes of this work to the practice of mineral flotation was described. In particular, it was found that the foamability was depressed in the presence of salt, especially at high concentration and for salt of high valency. A preliminary investigation on the foaming behaviour of surfactant mixtures suggested that synergism occurs in the presence of a molecularly cohesive, mixed surfactant monolayer at the air-liquid interface during the surfactant adsorption process. / Thesis (PhD)--University of South Australia, 2005.

Thesis (M.Sc.)--City University of Hong Kong, 2005. / At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Sept. 4, 2006) Includes bibliographical references.

Thesis (M.Sc.)--City University of Hong Kong, 2001. / "A dissertation submitted in part-fulfilment of the requirements for the degree of Master of Science of City University of Hong Kong." Title from title screen (viewed on Sept. 4, 2006) Includes bibliographical references.

Thesis (MSc)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (M.Eng.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Injection pressures available on commercial injection molding machines have increased from 10,000 to 20,000 psi with 40,000 psi in prospect. The pressure during solidification should strongly influence the crystallinity, and hence mechanical properties, of those regular polymers which can crystallize when cooled from the melt. In this study, samples of isotactic polypropylene were solidified under pressures up to 40,000 psi. In addition to tensile properties, the resultant density, microstructure and DTA structure were examined. From all measurements, it was concluded that the degree of crystallinity decreased with increasing solidification pressure. Spherulites formed under higher pressure were smaller in size and less branched than those formed at low pressure. Yield and tensile strengths were reduced as the solidi fication pressure was increased, the reduction being about 10% when solidi fication occurred at 40,000 psi. At first glance, these findings appear to predict strength differences within a particular molded part depending on the molding pressure used. It is concluded, however, that the strength variation would be less in a commercial part. The loss of pressure in the cavity as a result of freezing off at the in-gate should lead to a reduction in cavity pressure early in the solidification process, a lower mean pressure during freezing, and a relatively higher degree of crystallinity. / 2999-01-01

Nitroxide-mediated Controlled Degradation of Polypropylene <br /> Controlled-rheology polypropylene resins (CRPP) have been produced industrially for years using reactive extrusion processes employing peroxides as free radical initiators. The molecular weight characteristics of CRPP materials can be tailor-made depending on the final application in a very efficient and economic manner. <br /><br /> A PP-based nitroxide (NOR) with the trade name Irgatec CR76 has been recently developed by CIBA Chemicals, as a source of radicals and it is currently being evaluated for the production of CRPP. NORs are well-known as powerful stabilizers to protect plastics from the negative influence of light and heat, and easy in handling during processing. Preliminary experimental results exhibit a qualitative difference between Irgatec CR76 and other commonly used peroxides. <br /><br /> The purpose of this research work is to evaluate this new material as a potential replacement of commonly used peroxides in the production of CRPP. CRPP will be produced by reactive processing using varying amounts of Irgatec CR76 and the rheological properties of the materials produced will be investigated. By comparing results with Irgatec CR76 to those from other typical initiators, the effectiveness of Irgatec CR76 as an initiator will also be assessed. <br /><br /> The results of this research will have an impact not only on the potential extension of uses of the specific PP-based NOR (Irgatec CR76), but also, more generally, on the wider application of additives during degradation of PP. Potentially new materials can be produced with enhanced heat and light protection along with the other benefits inherent to standard CRPP.

Nitroxide-mediated Controlled Degradation of Polypropylene <br /> Controlled-rheology polypropylene resins (CRPP) have been produced industrially for years using reactive extrusion processes employing peroxides as free radical initiators. The molecular weight characteristics of CRPP materials can be tailor-made depending on the final application in a very efficient and economic manner. <br /><br /> A PP-based nitroxide (NOR) with the trade name Irgatec CR76 has been recently developed by CIBA Chemicals, as a source of radicals and it is currently being evaluated for the production of CRPP. NORs are well-known as powerful stabilizers to protect plastics from the negative influence of light and heat, and easy in handling during processing. Preliminary experimental results exhibit a qualitative difference between Irgatec CR76 and other commonly used peroxides. <br /><br /> The purpose of this research work is to evaluate this new material as a potential replacement of commonly used peroxides in the production of CRPP. CRPP will be produced by reactive processing using varying amounts of Irgatec CR76 and the rheological properties of the materials produced will be investigated. By comparing results with Irgatec CR76 to those from other typical initiators, the effectiveness of Irgatec CR76 as an initiator will also be assessed. <br /><br /> The results of this research will have an impact not only on the potential extension of uses of the specific PP-based NOR (Irgatec CR76), but also, more generally, on the wider application of additives during degradation of PP. Potentially new materials can be produced with enhanced heat and light protection along with the other benefits inherent to standard CRPP.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy