Perfluorocarbon groups, surfactants

When a hydrophilic functional group is attached to a perfluorocarbon chain the resulting fluorosurfactants (e. g. n-C F2 +iCOOLi, with n > 6) can reduce the surface tension of water from 72 dyn cm to 15-20 dyn cm compared to 25-35 dyn cm for analogous hydrocarbon surfactants [11],... 

A very different kind of surfactant molecule obtains if the carboxylate head group of an alkanoic acid is replaced by one that is both hydrophobic and lipophobic, like a perfluoroalkyl group. Such diblock molecules, F(CF2) (CH2) H(FmHn), have been shown to form normal and reverse micelles in perfluoroalkanes and alkanes, respectively [68,69]. On the bases of the well-known antipathy between hydrocarbons and perfluorocarbons, the disparity between cross-sectional areas and volumes of CH (18.5 and 10.22 A ) [70, 71] and CF (28.3 A and 16.04 A ) [70, 71] groups, and the tendency of long perfluoroalkyl chains to adopt helical conformations, it is expected and found that organized assemblies of FmH/i molecules exhibit some strange properties. For instance, the alkyl portions of many of these molecules melt before their perfluoroalkyl portions [72], and the allowed motions resemble closely those of -alkanes in their rotator phases [73, 74]. 

This section reviews the main experimental results for the exchange process and micelle formation/breakdown for solutions of pure surfactants, in the absence of additives other than salts. The surfactants considered are the conventional surfactants (one head group/one hydrocarbon chain and one head group/two hydrocarbon chains), the perfluoiinated surfactants (one head group/one perfluorocarbon chain), and the gemini (dimeric) surfactants (two head groups/two alkyl chains). 

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