Production of high internal phase emulsions using rising air bubbles

Abstract

High internal phase water in oil emulsions were produced by air sparging the two-phase system. The air sparging provided a mechanism for the incremental addition of the aqueous phase into the oil phase, and in turn the formation of aggregates of the aqueous droplets. Over time, a space-filling network of the droplets developed throughout the whole container. We refer to this critical state as a homogeneous, high internal phase coarse emulsion. Once the coarse emulsion was produced, the air bubbles were forced to perform useful work on the network, causing a refinement in the size of the droplets, with a concomitant increase in the emulsion viscosity. The emulsification process was reliable, however, over only a narrow range of air addition rates. At very low rates, the thin film drainage of the oil from between the aqueous droplets was more extensive, and hence the aqueous droplets coalesced and returned to the lower aqueous zone. At higher rates, the air flow tended to disrupt the droplet network. When expanded metal mesh was inserted into the vessel, with each horizontal layer of mesh separated by 40 mm, the process was found to be significantly more robust. Thus, using higher air rates, it was possible to achieve more than an order of magnitude increase in the emulsification rate. A well-defined coarse emulsion was also generated using gravity, by firstly causing aqueous phase droplets to detach from an upper surface, and secondly sediment to form a bed of droplets below. A given dispersed phase volume fraction was produced by fluidising the bed. Once the required bed concentration was formed, a refined emulsion was readily generated by air sparging