Water-nonionic surfactant systems, and the effect of additives

In this introductory article we approach microemulsions from the binary water-surfactant side. Model systems of the water - nonionic surfactant (C(i)E(j)) type are examined. Many features of microemulsions are observable in these binary systems. As such we discuss the dependence of the cloud points on i and j, the temperature dependence of the viscosity within the micellar phase, and the formation of dilute bilayer phases. The effect of additives is examined, as it permits to gain insight into the structures and interactions. Towards the end of the paper the most important additive for microemulsion formation, the oil, is considered. A special feature of long-chain surfactants is highlighted, namely, non-monotonic critical lines leading to very peculiar two-phase lobes as precursors to the formation of the three-phase bodies.