Effects of osmotic pressure on water transport in W1/O/W2 emulsions

In a W-1/O/W-2 double-emulsion globule, when the W-1 phase was made of pure water while salt (NaCl) was present only in the Wt phase, water was transported from W1 to Wt at a constant transport rate, -dR/dt. In the case of hydrated-surfactant transport, rates rose linearly with increasing salt concentration in Wt through acceleration of the dehydration process of the hydrated surfactants at the O/W-2 interface. When the water was transported through spontaneous emulsification and reverse micellization, the water transport rates were independent of the osmotic pressure over a significant range of salt concentration in W-2. When salt was present in both the W-1 and W-2 phases--though at a higher concentration in W-2-water transport stopped when the salt concentrations in W-1 and W-2 equalized, indicating that only water may transport through the oil phase while salt stays trapped in the W compartments. In visual-contact experiments, where transport was controlled by the hydrated-surfactant mechanism, the water transport rates were initially constant to then decreased asymptotically to zero. This showed that, as salt concentration in W-1 increased with time, the controlling process shifted from surfactant dehydration at the O/W-2 interface to hydration at the W-1/O interface. For the spontaneous emulsification and reverse-micellar mechanisms at visual noncontact, water transport rates remained constant during a given experiment and decreased with increasing initial salt concentration in W-1, indicating that the formation process of emulsified water droplets and reverse micelles at the W-1/O interface was the rate-controlling step, a zool Academic Press.