FORMATION MECHANISMS OF MONODISPERSED W/O EMULSIONS BY SPG FILTER EMULSIFICATION METHOD

The formation mechanism of monodispersed water-in-oil (W/O) emulsions by a Shirasu-Porous-Glass (SPG) filter emulsification method was investigated using various kinds of SPG filters of different pore diameters and copolymer-type surfactants. The size of the water droplets in the resulting emulsions and their dispersion stability strongly depended on the interfacial tension between water and oil phases, and stable monodispersed W/O emulsions were produced at an interfacial tension below 1 dyn cm-1. However, the sizes of the water droplets were smaller than the average pore diameters of each SPG filter used. It was suggested from calculations based on the mechanism of the drop volume (DV) method, one of the methods for determining the interfacial tension, that the size of the pore outlets of a filter is an important factor for determining the water droplet size rather than the average pore diameters determined by mercury porosimetry. This prediction was confirmed by the agreement of the outlet sizes of the pores calculated by the DV method and those estimated experimentally by a scanning electron microscope.