2. First formulation concepts for water-oil-surfactant systems

2.1 Composition variables and physico-chemical formulation variables

The formulation of microemulsions comes down to the choice of values for two types of variable: compositional variables and physicochemical formulation variables.

• Composition variables are the relative proportions of the system's main constituents: surfactant, water and oil. When these are pure, the properties of the mixture can be represented in a ternary water/oil/surfactant diagram, or expressed as a function of two independent variables: the water/oil volume ratio and the surfactant concentration. In practice, there are many more compounds and therefore more independent composition variables. To study such systems, we need to group the constituents into three pseudo-constituents...