Stabilization by a Lamellar Phase

Although many emulsions are stabilized by only one nearly saturated monolayer, this is not always the case. If the surfactant is balanced, it can form a lamellar phase (L ), co-existing with oil and water. If emulsification is performed in such a system, the emulsion droplets are often covered by several monolayers back to back, which drastically improves the emulsion stability. It should be noted that the original idea that emulsion drops must be stabilized by several monolayers back-to-back in order to be stable belongs to McBain.  

Friberg et al.attributed the stabilization effect of the nested lamellar layers to the change in dispersion attraction between emulsion droplets. Another interpretation is based on the hole nucleation in multilamellar films, originally proposed by de Gennes and Prost, and discussed below in more detail. 

12 Effect of Volume Fraction of Disperse Phase and Droplet 

Macroemulsions can be prepared in a very broad range of disperse phase volume fraction j , which is not limited by the close sphere packing value 0 = 0.74. Indeed, one can prepare a macroemulsion which contains only 1 wt% of continuous phase This can be done because liquid drops need not remain spherical and can pack into a structure, called a biliquid foam. 

When the effect of 0 on the emulsion stability is considered, one must distinguish between the effect of the volume fraction on the ease of emulsification and on the subsequent emulsion stability. The volume fractions of oil and water have a considerable effect on the ease of emulsification. For example, it is very difficult to prepare an OAV emulsion at an oil-to-water volume ratio of 9 1, even if an appropriate surfactant is selected. As a rule, the resulting system has an O/W/O type, which quickly converts into O/W plus excess oil after the mixer has been turned off. However, if the mixing cycle is repeated several times, or the oil is added not as a single batch but gradually, one can obtain a very concentrated and stable OAV macroemulsion. 

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