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of high HLB and low HLB give more stable emulsions than do single surfactants. Apart from the possibility of complex formation at the interface, the solubility of surfactant components in both the disperse and the continuous phase maintains the stability of the surfactant film at the interface from the reservoirs created in each phase. In the experimental determination of optimum HLB, creaming of the emulsion is observed and is taken as an index of stability. The system with the minimum creaming or separation of phases is deemed to have an optimal HLB. It is therefore possible to determine optimum HLB numbers required to produce stable emulsions of a variety of oils. Table 7.4 shows the required HLB of surfactants to achieve stability of five oils. A more sensitive method would be to determine the mean globule size in emulsions using modern techniques such as laser diffraction methods to produce data such as those in Fig. 7.13. For the mineral oil-in-water emulsion stabilized by a mixture of two

Table 7.4 Required HLB for different oils for o/w

emulsion formation

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