Coalescence lifetimes of oil and water drops at the planar oil-water interface and their relation to emulsion phase inversion.

We have measured the coalescence lifetimes of AOT-stabilised oil and water drops with the AOT monolayer present at the planar oil-water interface. Measurements were made as a function of aqueous phase NaCl concentration over the range over which phase inversion of the emulsions occurs and for heptane, dodecane and tetradecane as oil. The drop lifetimes decrease sharply with increasing [NaCl]. Below a crossover [NaCl], the oil drop lifetimes are longer than the water drops, whereas this behaviour is reversed at higher [NaCl]. The [NaCl] at the crossover points for the three oils increases with alkane chain length. This behaviour is compared with that of the corresponding emulsion systems which are water continuous at low [NaCl] but phase invert to give oil-continuous emulsions at high [NaCl]. The NaCl concentrations required for emulsion phase inversion increase with increasing oil chain length but are not identical to the [NaCl] values at the drop coalescence crossover points. [ABSTRACT FROM AUTHOR]