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Homogenizer treatment 0.5 h +

Ultrasonic treatement 0.5 h

Th-,

Figure 8. Particle size distribution of oil droplets in O/W emulsions prepared using the SPG membrane emulsification technique and conventional methods. [SDS] = 0.2 wt.% in water. Oil is kerosine. (Courtesy of Nakashima and Shimizu18)

The preparation of a monodispersed W/O emulsion is difficult compared to a O/W emulsion because the water droplets are difficult to stabilize by an electrical double layer repulsion force in an oil phase having a low dielectric constant (9,19). Therefore, it is preferable to choose an emulsifier such as macromolecular type surfactants which form a viscoelastic adsorbed film at the oil/water interface (2022). The author prepared a monodispersed W/O emulsion by using poly (oxyethylene-oxypropylene) copolymer type surfactants as an emulsifier. The surfactants were of PE-series and manufactured by the Sanyo Kasei Corp., Kyoto, Japan. The molecular formula of PE-series surfactant is H0(C2H4.0)n-(C3H60)7n-(C2H40)n-H and their average numbers of m and n are listed in Table 5. Deionized and distilled water was used after filtering through Millipore filter (220 nm). Toluene was used as an oil phase. Three kinds of SPG membranes, formed into a tube of 3 mm diameter and 0.6 mm film thickness having the different average pore sizes, were used. These are referred to as Membrane 1, 2 and 3 and used without further surface treatment (membrane surface is hydrophilic). The average pore diameters (Dp) of Membranes 1, 2 and 3 as measured by a mercury porosimetry were 0.98, 2.70 and 4.70 nm, respectively. The scanning electron micrographs of the SPG membrane surfaces were already shown in Figure 2. The volume ratio of water to toluene solution of surfactant was fixed at 1:10, and emulsification was performed at room temperature. The PE-series surfactants were dissolved in toluene before use.

Table 5

Properties of PE-series surfactants

Table 5

Properties of PE-series surfactants

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