Visualization of water transport in W-1/O/W-2 emulsions

Water transport between two aqueous phases and through an intervening oil p hase under osmotic pressure was observed and quantified visually using capi llary video-microscopy. Under certain conditions. a new mechanism was obser ved directly, according to which the pure-water phase emulsifies spontaneou sly and the resulting emulsified droplets migrate to the saline aqueous pha se. Another Ending was the importance of the thickness of the oil phase, O, that separates two aqueous bodies, W-1 and W-2, in that it determines whic h transport mechanism of water between W-1 and W-2 will be predominant. Spe cifically, in a W-1/O/W-2 emulsion globule where W-1 represents the interna l pure-water droplets and W-2 the suspending saline-water medium, when W-1 and W-2 were at visual contact, water transport occurred mainly through the hydrated surfactant mechanism. In the case of a visible minimum distance o f separation between W-1 and W-2, measuring from a few to over 100 mu m, th e water transport rate was found to be significantly lower than the rate at visual contact and water migration occurred via spontaneously emulsified d roplets and reverse micelles. In all cases, the transport rate was independ ent of the size of the water droplets and the oil globule, and in the case of no visual contact, it was also independent of the minimum separation dis tance between W-1 and W-2. This result implies that, under the experimental conditions used, the water transport rate in W-1/O/W-2 emulsions is contro lled by interfacial processes, rather than being diffusion controlled as ha s been suggested by previous work. (C) 2000 Elsevier Science B.V. All right s reserved.