Partially fluorinated surfactants

Fig. 2.4. CMC of various hydrocarbon, fluorocarbon and partially fluorinated surfactants as a function of the fluorine-to-hydrogen ratio. CMCs are given relative to those of the hydrocarbon surfactants. Solid line is a suggested ideal behavior (From Ref.25 )...

Figure 10 Echo intensity vs. the parameter q for the water in a concentrated W/O emulsion consisting of a partially fluorinated surfactant, perfluorodecaline, and water. (Figure adapted from...

Partially fluorinated surfactants have several advantages with respect to their per-fluorinated counterparts, due to the low solubility of fuUy fluorinated chains in hydrocarbons. The hydrocarbon segment of a partially fluorinated surfactant provides solubility in commonly used organic solvents, lowers the melting point of the surfactant, reduces volatility and decreases the acid strength of perfluorinated acids [51]. 

The hydrophobes of partially fluorinated surfactants contain both fluorine and hydrogen atoms. Unlike the hydrophobe of hydrocarbon surfactants, the partially fluorinated hydrophobe consists of two mutually phobic parts which are not compatible. Partially fluorinated surfactants therefore exhibit anomalies in macroscopic characteristics, such as the critical micelle concentration (cmc), and in microscopic phenomena as well. 

Klevens and Raison [65] studied micellization of sodium dodecyl sulfate and perfluorooctanoic acid. Their data have been reviewed by Mukerjee and My-sels [66], who concluded that partially fluorinated surfactants behave like mixtures of fluorinated and hydrocarbon-based surfactants. 

Thoay [101] studied interfacial activity of partially fluorinated surfactants in an oil-water medium. The fluorocarbon group was located either at the end of the hydrocarbon tail, inserted in the middle of the hydrocarbon chain, or attached as a branch to a conventional hydrocarbon-type cationic surfactant. Three types of surfactants were used ... 

Partially fluorinated surfactants exhibit at least two apparent anomalies [1) ... 

Both facts are in accord with the mutual phobicity of hydrocarbons and fluorocarbons, evidenced by the limited mutual solubility and the nonideality of the solutions [1]. This mutual phobicity reduces micellization of partially fluorinated surfactants and explains the aqueous environment of the terminal [Pg.243]

For a cationic partially fluorinated surfactant DEFUMAC, having the structure C8F,7CH2CH(0H)CH2NCH3 (C2H40H)2 Cr, Tamori et al. [195] found the... 

Partially fluorinated surfactants also have been investigated by NMR. Muller and Birkhahn [27] found the fluorine chemical shift for anionic terminally fluorinated surfactants, CF3(CH2)sCOONa and CF3(CH2)ioCOONa, to be essentially independent of ionic strength. An added electrolyte depressed cmc but did not affect the chemical shifts for the surfactant anions in the micelle. They explained their results by the formation of prolate-shaped spheroid micelles in the presence of sufficient electrolyte. An alternative explanation that electrolytes do not increase the micellar size was considered to be unlikely. 

Raman spectroscopy has been very useful for conformation studies of hydrocarbon-type and partially fluorinated surfactants but has only a limited value for perfluorinated surfactants. Unlike a strong IR absorption band arising from the CF stretching mode, the intensity of Raman bands is low for these vibrations. In contrast to the characteristic CH stretching mode, the CF and CF2 modes are in a region where other molecular modes occur and complicate absorption patterns. Amorim da Costa and Santos [72] have nevertheless been able to show Raman spectroscopy to be useful for structure and conformation analysis of fluorinated surfactants (Fig. 9.6). 

---