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Title: A study of particulate foams
Author: Wilson, J. C.
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 1981
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This research project investigated particle-fluid interactions at the air-water interface, thus enabling the important factors involved in the formation of particle stabilised foams to be understood. It was hoped that this would lead to an understanding of the behaviour of aerated milk products which are stabilised by milk fat globules. Experiments were devised to simulate the properties of the globules at the interface, in particular their wetting and dewetting behaviour, and to determine the structure of foam films formed in particulate systems. For this purpose a model system, polystyrene latex particles having diameters in. the range 1- 4 qua, was used. The following conclusions were reached. Polystyrene particles will not foam when suspended in water alone. Particulate foams were only formed when the system approached the conditions required for bulk coagulation. Two foaming systems have been isolated; one where instability of the bulk phase was the result of increased ionic strength and the other was the result of specific adsorption of ions. The structure of the foam film has been postulated as a bilayer of latex particles, the particles in each monolayer being hexagonally closepacked. Within each monolayer the particles appear to be in positions of the primary minimum energy, whilst in the adjacent layers they are situated in positions of the secondary minimum. The monolayers have been found. to be rigid and solid-like in character. A particle size effect exists, latices having diameters of I pm were reluctant to foam. Following from this the calculated interaction energy and strength of the monolayer increased with particle size. The mixed particle size monolayers indicated the formation of a more liquid-expanded film illustrating the weakening of the monolayer due to the presence of smaller particles.The contact angle data indicated an increase in contact angle to give angles greater than 900 within the foaming regions for both foam systems studied. Therefore the particles must acquire a hydrophobic nature to make it energetically favourable to be situated at the air/liquid interface as compared to the bulk. By so doing a latex stabilised foam was formed
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available