Surface tension in organic liquids

Many fluorochemicals are remarkably surface active in organic liquids [81-85] Scholberg et al. [50] found that perfluorocarboxylic acids lower the surface tensions of organic solvents more than any other chemical ever reported. 

Ellison and Zisman screened various compounds for surface activity in organic liquids by using a Langmuir film balance. The compound was spread on an organic liquid and the surface film pressure measured as a function of surface area [85]. The results indicated that the surface activity of fluorinated compounds in organic liquids can be predicted approximately from the Harkins equation for the spreading coefficient  

The effect of surfactants on surface tension is much smaller in solvents than in water. Surfactants can lower the surface tension of water by more than 50 mN/m, to below one-quarter of its original value. In aromatic hydrocarbons, only a few fluorinated surfactants can decrease the surface tension to half of the initial value. The surface tension depression is smaller, mainly for two reasons. First, the initial surface tension of solvents, 19-30 mN/m for hydrocarbons, is lower to start. Second, surfactants are not as effective in organic media as in water because ad- 

The structural requirements for a surfactant in an organic liquid are quite different from the structures of typical fluorinated surfactants used in water. In order to function as a surface-active agent, a compound has to be amphiphilic and consist of lyophobic (solvent insoluble) and lyophilic (solvent soluble) groups in the molecule [86]. In water, the hydrophobic group of the surfactant causes a re- 

In aqueous solutions of nonfluorinated surfactants, the lowest surface tensions are attained by covering the surface with a close-packed monolayer of vertically oriented hydrocarbon chains forming a continuous layer of —CH3 groups exposed to air [89]. By analogy, the surface tension of a solution of a fluorinated 

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