An emulsion is a dispersion of one immiscible phase, such as oil, in another phase, such as water. Nowadays, the term is used to describe droplets of the dispersed phase without any limits on the diameter (size) of those drops. Whereas some time ago emulsions were only used to describe drop sizes generally below 10 microns (i.e. 0.01 of a millimeter). For food emulsions, such as water drops inside a cocoa butter or chocolate phase, the drop size of the water should be well below 30 microns - otherwise you might feel a gritty sensation due to the dispersed water drops.
Membrane emulsification can be used instead of homogenisers and there is no need for an 'emulsifier', which is commonly used to reduce the interfacial tension between the phases encouraging drop formation by reducing the amount of energy (turbulence) to form the drops. Instead the drops are formed physically by passage through the membrane and shear in the continuous phase at the membrane surface, which shears off the drops from the membrane. A 'stabiliser' is still required though - as once the drops have been formed they must be kept apart and from coalescing.
The illustration on the right shows an oil phase being injected in to a water phase, where the shear at the membrane surface comes from the crossflow of the continuous phase over the membrane surface: hence the term crossflow membrane emulsification.
In the absence of shear at the membrane surface the drops will continue to grow, until they possibly detach due to their natural buoyancy force overcoming the capillary force holding them to the membrane. The lower picture on the right shows large drops emerging from a membrane. Click on the picture or this link to see a video (wmv format and 205 kB size)of this process.
If you would like to see more information on the membranes used for this process of membrane emulsification, please see this explanation.
If you would like to see how the process of continuous coacervation works, using membrane emulsification, please see this explanation.
