Development of W/O/W-type dispersion during phase inversion of concentrated W/O emulsions

It has been found that the development of a W/O/W-type dispersion precedes phase inversion of concentrated W/O emulsions in the presence of hydrophilic emulsifier in the aqueous phase. This phenomenon was examined with a mixture of liquid paraffin and water using Span 80 in the oil phase and SDS, CTABr, or Tween 80 in the aqueous phase. The W/O/W emulsion formation was assessed by comparing the extent of the oil layer in a unit volume of the samples with each other, which was estimated from the viscosity changes in the diluted sample under the concentration gradients of glucose between the inner aqueous phase and the aqueous suspending fluid. The development of a W/O/W-type dispersion could be observed when the volume fraction of the aqueous phase was higher than 0.7, while another factor affecting the W/O/W emulsion formation was the molar ratio of the Span 80 to the hydrophilic emulsifier in the sample. In the case of SDS system, the range of the W/O/W emulsion formation appeared more widely in the molar ratio (i.e., from 4 to over 60) than that of CTABr or Tween 80 systems, so that the use of SDS facilitated the development of a W/O/W-type dispersion. The oil layer in the W/O/W emulsions provided by the phase inversion phenomenon was stable for at least a month when stored.