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Title: Crystallisation in emulsion and microemulsion systems
Author: Nicholson, Catherine Emma
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 2006
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The use of emulsions as an aid to the study of crystallisation has long been known. However, the exploitation of this technique has not yet been realised to its full potential. The various conditions that can be generated at, or near, an interfacial region provide a wide range of possibilities for the controL and probing of crystallisation mechanisms. In this thesis, the effect of the interfacial curvature is considered for the case of ice crystallisation within water-in-oil emulsions. The use of a known ice nucleator, heptacosanol, acting as a co-surfactant enables the effect of a reduced epitaxial match to be monitored, with decreasing water pool diameter. The extreme case where the water pool does not contain enough material to form a crystalline nucleus such that ~G ~ 0 on complete crystallisation is found. This demonstrates for the first time that a direct experimental measurement of the critical nucleus size is possible. The use of non-ionic surfactants allows emulsions to phase invert from water-in-oil to oil-in-water upon cooling, and on passing through the phase inversion, ultra low interfacial tensions are obtained. At the phase inversion, crystallisation by the surfactant layer is found to be greatly inhibited, even at high solute supersaturations for glycine and L-asparagine emulsions. Hence we achieve anomalous crystallization behaviour, with crystallisation achieved both on cooling and heating from the same system. Another unique effect characterised is that of oil droplet inclusion into a single crystal. The highly polar octanoic acid oil phase adheres to the growing glycine crystal so strongly that crystal growth proceeds around the droplet without disruption to the overall resulting crystal to produce macroporous crystals. Where growth rates are uneven, highly fenestrated single crystalline structures result. Upon reducing the oil droplet diameter, dendritic morphologies, highly unusual for such low supersaturations of glycine, are formed. Moreover, the surfactant mixture also controls the polymorph produced, and reproducibly yields the desired ~-glycine form.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available