Fluorinated Surfactants Without a Hydrophile

Surfactants are used most frequently in aqueous systems. Their amphiphilic character arises from the presence of a hydrophilic group and a hydrophobic group in the same molecule. A perfluoroalkyl group of fluorinated surfactants is not only hydrophobic but oleophobic as well. In a hydrocarbon medium, a perfluoroalkyl 

Semifluorinated alkanes are low-molecular-weight block copolymers of nonnal perfluorocarbons and hydrocarbons [160-171]. Their structure formula F(CF2) (CH2) H is usually abbreviated to F ,H [164] or F H , [163]. The semifluorinated alkanes so far reported have 6 to 32 carbon atoms m -f- n). 

The compounds w = 12 and n = 8, 14, or 18 lower the surface tension of n-dodecane [164]. The adsorption of the semifluorinated alkane at hydrocarbon-air surfaces increases with increasing length of its fluorocarbon chain [172], increasing chain length of the alkane solvent and decreasing temperature [169]. 

The polymeric surfactants (HFPO) Ar, where (HFPO) is a hexafluoro-propylene oligomer and Ar an aryl group [52,173], lower the surface tension of hydrocarbons such as w-xylene and belong, therefore, to the class of hydrophile-free surfactants (see Section 1.9). 

The semifluorinated alkanes, such as FeHio, stabilize aqueous perfluoro emulsions by forming an interface between the fluorocarbon phase and the phospholipid emulsifier [174]. The stabilizing effect is attributed to a more favorable structure of the interfacial film [175]. 

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Oleophilic/oleophobic fluorinated surfactants without a hydrophile, designed for use in hydrocarbon systems, are in a structural sense also nonionic fluorinated surfactants (see Section 1.8) for example, the semifluorinated alkanes [266-270], block polyethylene-polypropylene glycol ethers prepared with perfluoroalkene trimers [271], surfactants featuring an oligo(hexafluoropropene oxide) chain [272], and carboxamides and sulfonamides derived from A -(perfluorooctanesul-fonyl)piperazine [273]. 

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