Critical micelle concentration fluorinated hydrocarbons

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. 

Critical micelle concentrations of fluorinated surfactants are approximately equal to those of their hydrocarbon analogs with a 1.5-1.8 times longer... 

In analogy to surfactants with a hydrocarbon chain, the critical micelle concentrations for fluorinated surfactants in an aqueous solution depend on the fluorocarbon chain length and the counterion (Table 6.9) [58,59,75,77,96,139, 146-154] and decrease with increasing hydrophobe chain length. 

The critical micelle concentrations of fluorinated surfactants are compared with those of hydrocarbon surfactants in Table 6.11 [59,157]. The cmc values for C7 and Cg fluorinated surfactants are approximately equal to those for Ci 1 and C12 hydrocarbon surfactants, respectively. The greater hydrophobicity of the fluorocarbon chain enhances the amphiphilic character of the surfactant and increases surface activity, reflected in surface tensions below 20 dyn/cm and lower cmc values [1,159]. Perfluorination reduces cmc values about four times per —CF2— group. The A value [or K value in Eq. (35)] does not change considerably with the type of the surfactant. Because the relation expressed by Eq. (34) is exponential, the cmc value of a fluorinated surfactant is approximately equal to that of a hydrocarbon surfactant with a hydrocarbon chain 1.5-1.7 times longer than the fluorocarbon chain [59,157,160]. 

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