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.
| Identifer | oai:union.ndltd.org:ADTP/267470 |
| Creators | Tan, Su Nee. |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | copyright under review |
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