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Frothers are used in flotation to aid generation of small bubbles, but little is known about the mechanisms that take place in the flotation machine to produce such an effect. Coalescence prevention is the common explanation, although the exact mechanism is obscure and almost no attention has been paid to a frother effect on bubble break-up, the other possible mechanism. This thesis presents a technique to study the effect of frothers on bubble coalescence at the generation stage (at a capillary tube) and a technique to study the effect of frothers on bubble coalescence and break-up in a turbulent field. The first technique is based on the sound bubbles emit when they form and coalesce. The sound signal was linked to bubble formation and coalescence events using high-speed cinematography. The technique has a resolution capable of detecting coalescence events that occur within 1-2 ms. The second technique allows discriminating between coalescence and break-up and is based on the exposure of a mono-size distribution of bubbles to a turbulent field generated by a three-bladed axial flow impeller. Analysis of bubble size distributions after contact with the turbulent field gives the coalescence and break-up fraction. The results show frothers reduce coalescence and alter the bubble size distribution of bubbles generated by break-up. / In the course of high-speed imaging an effect of frother on bubble shape and motion after formation was detected. Analysis of this forms the third major component of the work. A dependence of velocity on bubble aspect ratio is shown, which is in line with recent literature.

The potential of surfactants for improving the yields of alpha-amylase during the solid substrate fermentation (SSF) of potato starch using pure and mixed cultures was examined. The microorganisms used in this study were Aspergillus oryzae ATCC 1011, Bacillus subtilis ATCC 21556 and Bacillus subtilis ATCC 21332. The surfactants tested were Tween 20, Tween 80, SDS and surfactin. The fermentations were carried out in perforated trays after the addition of 10% (v/w) inoculum and with temperature and humidity controlled at 30°C and 90% RH respectively. Samples were taken and analyzed quantitatively for the production of alpha-amylase and biomass and qualitatively by scanning electron microscopy (SEM) using a JSM-840 A scanning microscope at 10 kV accelerating voltage. / It was possible to increase fungal alpha-amylase production by as much as 6 fold in the process with the addition of either synthetic surfactants or the biosurfactant surfactin. The bacterial alpha-amylase yields increased up to 11.5 fold in with the addition and/or the co-culture production of surfactants. The highest enzyme activity was found in the fermentation of a mixed culture of the two Bacillus strains with the addition of Tween 80. During the SSF with B. subtilis ATCC 21332 and ATCC 21556 as a mixed bacterial culture, there was also the production of surfactin in yields comparable to those obtained in a submerged fermentation. The biofilm formation as observed by SEM appeared to be associated with the presence of surfactants in the process and was not formed when no surfactants were present. The biofilm was observed as an entrapment of the bacteria in the substrate, resulting in improved access to the starch and higher production of alpha-amylase.

Bibliography: leaves 209-254. / viii, 254, [39] leaves, [17] leaves of plates : ill. 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Attempts to construct an evolutionary overview of the regulation of surfactant secretion among the vertebrates. A detailed whole animal and in vitro study of the factors that control surfactant secretion and function in the central Australian agamid lizard Pogona vitticeps was undertaken. Type II pneumocytes were also isolated and cultured from Australian lungfish, North American bullfrogs and fat-tailed dunnarts. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physiology, 1999

Thesis (Ph. D.)--School of Chemistry, Faculty of Science, University of Sydney, 2003. / Bibliography: leaves 117-121.

Thesis (M.Ch.E.)--University of Delaware, 2008. / Principal faculty advisors: Norman J. Wagner, Dept. of Chemical Engineering; and Eric W. Kaler, College of Engineering. Includes bibliographical references.

Thesis (Ph. D.)--University of Sydney, 2005. / Title from title screen (viewed 22 May 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Chemistry, Faculty of Science. Includes bibliographical references. Also available in print form.

Thesis (Ph. D.)--University of Sydney, 2003. / Title from title screen (viewed Apr. 28, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Chemistry, Faculty of Science. Degree awarded 2003; thesis submitted 2002. Includes bibliography. Also available in print form.