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Title: Studies of creaming, flocculation and crystallisation in emulsions : computer modelling and analysis of ultrasound propagation
Author: Pinfield, Valerie Jane
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 1996
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The processes of creaming, flocculation and crystallisation are important factors in the stability and properties of food emulsions. Measurements of the ultrasound velocity and attenuation in an emulsion are used as a non-destructive probe of emulsion behaviour. The present work aims to increase the understanding of the destabilisation processes themselves and to improve the techniques for interpretation of ultrasound measurements on such systems. These aims were addressed through the computer modelling of creaming, flocculation and crystallisation behaviour, and through the investigation of theories for interpreting ultrasound measurements Two computer models have been developed of creaming in emulsions, both with and without flocculation. One takes a phenomenological approach, and is able to predict macroscopic concentration profiles of emulsions. The other is a small-scale simulation at the level of individual particles. The results of the phenomenological model are in qualitative agreement with experiment al results in the absence of particle interactions The effects of flocculation on creaming behaviour were not however, reproduced by the model. The small -scale simulation demonstrated that a simplified model of flocculation and creaming could result in features in the concentration profiles which are comparable with those observed experimentally. However, some aspects of creaming behaviour were not reproduced by either model. The investigation of theories of ultrasound propagation in emulsions concluded that multiple scattering theory is appropriate for the typical emulsions studied. The complex calculations required by the application of the theory are simplified in some special limits, which are presented. Alternative, practical, techniques are presented for the interpretation of ultrasound measurements. These are based on scattering theory but utilise experimental determination of the scattering properties of the emulsion, so avoiding the difficulties associated with multiple scattering theory calculations. The methods which have been developed are particularly relevant to creaming and crystallisation studies. The effects of particle size variation in emulsions can influence the interpretation of ultrasound measurements, and restrictions are therefore placed on the application of the methods.
Supervisor: Dickinson, Eric ; Povey, Malcolm Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available