Wettability of solid particles in relation to particle-stabilised foams and emulsions

Colloidal particles and surfactants are commonly used, either individually or combined, as stabilisers of emulsions and foams. While the properties of surfactants and particles under a range of conditions and concentrations are relatively well known, there are some areas that require further investigation. The wettability of colloidal particles is one of the main factors that determine how they behave in a given system but determining the wettability is difficult due to the small size of the particles. The Film Calliper Method (FCM) has been proposed as a simple technique for the direct measurement of the contact angles of micrometer and submicrometer particles in their natural environment. One of the main aims of this work was to develop the Film Calliper Method for measuring contact angles at oil -water interfaces. The FCM was therefore used to measure the contact angles at oil - water interfaces for a range of particles, such as latex and silica particles, in different systems. For the first time directly measured contact angles are linked to the types of emulsions stabilised by the particles. The FCM was also used to directly measure the contact angles of silica particles in cationic surfactant solutions at air and oil interfaces for the first time. The stability of foams and emulsions made with particle - surfactant mixtures were investigated and related to the particle contact angles. Janus particles are a special category of particles which have different properties on each hemisphere. A method for making Janus particles was developed using template silica particles masked with a polymerised Pickering emulsion. The portion of surface exposed for treating can be tuned by controlling the inherent wettability of the template particles as proven with fluorescence microscopy. Emulsions stabilised by amphiphilic Janus particles made with the method are compared with emulsions stabilised by homogeneous particles with similar wettability.EThOS - Electronic Theses Online ServiceEngineering and Physical Sciences Research Council (Sponsor)GBUnited Kingdo