INCORPORATION OF HYDROCARBONS INTO SURFACTANT MONOLAYERS

Alkane incorporation into close-packed surfactant monolayers at oil-water interfaces can greatly influence the surface concentration of surfactant, depending on the chain length of the alkane. Such incorporation into monolayers stabilising microemulsion droplets in Winsor systems (microemulsions in equilibrium with excess of the dispersed phase) can cause an inversion of the microemulsion type from oil-in-water to water-in-oil or vice versa. Closely related to this are the effects which solubilised hydrocarbon can have on the cloud points of aqueous solutions of nonionic surfactants. It is difficult to measure quantitatively the extent of hydrocarbon incorporation into surfactant monolayers at oil-water interfaces, but we have determined the extent of uptake of a range of alkanes into monolayers of various surfactants at the air-water surface. In this paper we consider close-packed monolayers at both planar and curved (microemulsion droplet) interfaces, and the effects which incorporation of hydrocarbons into the monolayers has on system behaviour. The extent to which mixed alkane+surfactant monolayers resemble monolayers at oil/water interfaces is explored, and for one system we show how alkane incorporation into films at A/W surfaces directly mirrors microemulsion behaviour in the same system. © 1990.