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* monodispersity ratio, U=Di/D2, where Di and D2 are weight-, and number-mean diameter of water droplets, respectively.

Figure 10. Plots of average diameter of water droplets (Dw) prepared by Membrane 3 as a function of interfacial tension

Interfacial tension, dyne/cm

Figure 10. Plots of average diameter of water droplets (Dw) prepared by Membrane 3 as a function of interfacial tension

(b) Pore Size and Structure

The influence of Dp on Dw are compared at different PE-64 concentrations in Figure 11. The Dw increases with increasing Dp, but the extent of increase is reduced above Dp of 2.7 |xm (Membrane 2) and no remarkable difference can be observed between Membranes 2 and 3. This result corresponds to the result that Membranes 2 and 3 gave similar Pc (see Table 7). If Dp is a dominant factor to determine Dw, Dw should be directly proportional to Dp. From this paradox on the relationship between Dw and Dp, other factors must be considered.

The drop volume (DV) method, one of the methods used in determining the interfacial tension, is helpful to describe this point because the mechanism of the DV method is very similar to that of the SPG membrane emulsification. In the DV method, the droplets of liquid 1 are formed through the tip of the capillary into a surrounding fluid (liquid 2) as shown in Figure 12. The DV method consists of measuring the volume of a droplet that just detaches vertically itself from the horizontal tip of a sharply cut and polished capillary of accurately known outer diameter. Harkins and Brown (23) showed that the interfacial tension (y) is related to the droplet volume (V) and the outer capillary diameter (D) by the equation (4);

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