Surfactant Properties of Semifluorinated Alkanes in Hydrocarbon and Fluorocarbon Solvents

The phase behaviour and aggregation of the semifluorinated alkane F‐(CF 2 ) 8 ‐(CH 2 ) 16 ‐H (abbreviated to F 8 H 16 ) in hydrocarbon and perfluorinated solvents has been investigated. The variation of solubility with temperature for F 8 H 16 in perfluorinated solvents shows highly non‐ideal behaviour and exhibits a sharp increase at a temperature a few degrees below the melting point of F 8 H 16 . The behaviour is similar to that in the region of the Krafft point of a conventional surfactant in water. With iso ‐octane as solvent, the solubility shows only slight deviations from ideal behaviour. Vapour pressure osmometry (VPO) results confirm the near ideal behaviour of F 8 H 16 in iso ‐octane. For F 8 H 16 in perfluorodecalin at 38 °C, VPO results show that aggregates are formed at concentrations above approximately 0.02 mole fraction. The aggregation number is 6 and is virtually independent of the SFA concentration. The results are discussed in terms of the antipathy between hydrocarbons and fluorocarbons as reflected in the values of the upper critical solution temperatures (UCST) of binary mixtures of hydrocarbons with perfluorinated solvents.