SHEAR-INDUCED PHASE INVERSION AND SIZE CONTROL OF WATER OIL-WATER EMULSION DROPLETS WITH POROUS MEMBRANE

A water/oil/water (w/o/w) emulsion was prepared with liquid paraffin, hydrophobic (Span 80) and hydrophilic (Tween 20) surfactants. When the emulsion was extruded through a polycarbonate membrane possessing pores of 3 or 8 μm in diameter, the extruded emulsion became semisolid. This semisolid emulsion proved to be a w/o emulsion judging from dispersibilities into water and chloroform, changes in percentages of trapped markers initially added to inner and outer aqueous phases, and observation of electron microscopic photographs. The semisolid w/o emulsion possessed smaller aqueous droplets than the original w/o emulsion at the first emulsification step and was easily redispersed into a hydrophilic surfactant aqueous solution. The resultant redispersed emulsion was a w/o/w type and its droplet size was smaller and more homogeneous than the original w/o/w emulsion. This semisolidification phenomenon caused by phase inversion was affected by the membrane materials and molecular ratio of hydrophilic and hydrophobic surfactants. © 1991 Academic Press, Inc.