Internal Coalescence as a Mechanism of Instability in Water-in-Oil-in-Water Double-Emulsion Globules

Abstract

Using capillary microscopy, internal coalescence between the internal aqueous compartments in a single water-in-oil-in-water (W1/O/W2) double-emulsion globule was investigated. Globules were prepared using either sodium dodecyl sulfate (SDS) (ionic) or Tween 80 (nonionic) as the water-soluble surfactants and Span 80 as the oil-soluble surfactant. Concentrations of both the hydrophobic and hydrophilic surfactants were varied until coalescence between the internal aqueous droplets was observed. Internal coalescence was observed when the concentration of SDS or Tween 80 in the internal aqueous phase was 1−3 CMC (critical micelle concentration) or 50−100 CMC, respectively, and occurred preferentially when the concentration in the internal phase was significantly greater than in the external phase. Internal coalescence always occurred in conjunction with coalescence between the internal W1 and external W2 aqueous phases (external coalescence). When W1 and W2 were not too dissimilar in their overall surfactant ...