Selection of Surfactants for Microemulsion Formulation

The PIT system provides information on the type of oil, phase volume relationships and concentration of the emulsifier. The PIT system is established on the proposition that the HLB number of a surfactant changes with temperature and that the inversion of the emulsion type occurs when the hydrophilic and lipophilic tendencies of the emulsifier just balance. At this temperature no emulsion is produced. From a microemulsion viewpoint the PIT has an outstanding feature since it can throw some light on the chemical type of the emulsifier needed to match a given oil. Indeed, the required HLBs for various oils estimated from the PIT system compare very favourably with those prepared using the HLB system described above. This shows a direct correlation between the HLB number and the PIT of the emulsion. 

As discussed in Chapter 6, the CER concept provides a more quantitative method for selecting emulsifiers. The same procedure can also be applied for microemulsions. 

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