Evolutionary behaviour of miniemulsion phases: II. Growth mechanism of miniemulsion droplets

The growth mechanism of droplets of hexadecane-in-water emulsions stabilize d by heptaethylene glycol mono-n-dodecyl ether was studied by means of phot on correlation spectroscopy. When the water-to-oil ratio (WOR) was varied f rom 4 to 10, a translucent oil in water emulsion (a so-called 'miniemulsion ') was obtained, while an opaque oil in water emulsion (O/W emulsion) was p repared when WOR was equal to 3. The z-average hydrodynamic radius of dropl ets, r(z), was measured over the 24 days after preparation. Plotting the cu be of the z-average radius as a function of time, we found that r(z)(3) var ies linearly with time in the system of the O/W emulsion (WOR = 3). This su ggests that the process by which the droplets grow is that of Ostwald ripen ing. On the other hand, the same plot for the system of miniemulsions (4 < WOR < 10) shows two regimes in the process. In both regimes, r(z)(3) varies linearly with time. The rate obtained for the earlier stage is smaller tha n that of the latter stage. The droplet size distribution became too broad compared with the prediction of Lifshitz-Slezov-Wagner theory for Ostwald r ipening similar to 10 days after preparation. Then it approached the predic ted distribution again similar to 20 days after preparation.