Coalescence at rest and during flow was studied in emulsions of paraffin oil in water with several surfactants and with crystals of solid paraffin or tristearate in the oil phase. Solid fat in the oil phase was estimated by pulsed nuclear magnetic resonance. Without crystals, oil-in-water emulsions were mostly stable and flow hardly influenced coalescence, even of unstable emulsions. Emulsions with crystals in the dispersed oil phase were less stable if crystals appeared at the interface. The contact angle indicated that crystals could be oriented in the interface; if so, instability was promoted by creaming, Couette flow, turbulence or flow with Taylor vortices. Coalescence in such systems could be caused by crystals sticking through the interface and piercing the film between the globule and a second approaching globule. The effect of variables such as type of surfactant, type of crystal, amount of crystalline fat, globule size, volume fraction of fat and ionic strength fitted this view. Natural cream with part of the globular fat crystallised behaved to some degree like the model systems but there were deviations.
|Qualification||Doctor of Philosophy|
|Award date||26 Sep 1980|
|Place of Publication||Wageningen|
|Publication status||Published - 1980|
- fluid mechanics