Kinetic Theory of Macroemulsion Type

In general, hydrophilic groups in the interfacial film constitute a barrier to the coalescence of oil droplets, whereas hydrophobic groups in the interfacial film constitute a barrier to the coalescence of water droplets. Hence an interfacial film that is predominantly hydrophilic tends to form O/W emulsions, whereas one that is predominantly hydrophobic tends to produce W/O emulsions. 

According to Davies, a rate of 10-2 times the collision factor (i.e., Ae E/kT = 10 2 A in equation 8.9) is a fast rate of coalescence, corresponding to complete coalescence of that phase within an hour, whereas a rate of 10-5 A is a very slow rate, corresponding to a stability of the order of several months for that phase in a dispersed form. Therefore, if the rate of coalescence of one phase is of the order of 10 5 A and the rate of coalescence of the other phase is considerably faster, then a stable emulsion will be formed with the phase having the slower rate as the dispersed phase. On the other hand, if the rate of coalescence of both phases is of the order of 10 2A, then both phases will coalesce rapidly and the emulsion will break, regardless of which phase has the slower rate. 

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