Mutual phobicity

However, no systematic investigation of adsorption and micellization of the alcohol-fluorocarbon (FC) surfactant mixture has been made. Other studies have examined the "mutual phobicity" between the hydrocarbon (HC) and FC chain in the mixed system of FC and HC surfactants (5-10) It is expected that "mutual phobicity" should be observed in the alkyl alcohol-FC surfactant system.too. In this... 

The j6f-values are all positive, which is to say, the activity coefficient of the surfactants in the surface phase are greater than 1, clearly indicating the "mutual phobicity" between FC- and HC-chains of the surfactants. However, the positive values ofySg- are considerably small, showing a rather weak mutual-phobic interaction. 

The rather great value of shows the strong molecular interaction between the two components polar groups since the two hydrophobic chains would be mutual-phobic, pm value calculated by equation cl 7)also shows this pointi... 

The nature of surface adsorption and micelle formation of various mixed FC- and HC-surfactants systems can be conveniently and well investigated by the non-ideal solution theory semi-emplrlcally applied in the surface layer and micelles. The weak "mutual phobic" interaction between FC- and HC-chains has been clearly revealed in the anionic-anionic and nonlonic-nonionic systems as Indicated by the positive values. value cannot be obtained... 

In the systems with considerable molecular interactions between the two surfactant components, such as CgNBr-CyFNa (cationic-anionic) and CsSOC-CrFNa (nonionic-anionic) systems, the "mutual phobic interaction" can be concealed entirely and there are large negative jSg. and /3m values for these systems. 

Perfluoroalkyl chain surfactants are much poorer wetting agents than alkyl chain surfactants for both paraffin and polymethyl methacrylate surfaces (Pyter, 1982). One explanation may be the mutual phobicity of alkyl and perfluoroalkyl chains, causing perfluoroalkyl chain surfactants to be adsorbed more poorly than alkyl chain surfactants at these solid-aqueous solution interfaces. 

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. 

A mixed monolayer can be considered an ideal monolayer when the surface pressure tt is near zero. Zhang et al. [46] suggested that at near-zero surface pressure, mixtures of mutually phobic surfactants indeed form ideal monolayers. As... 

Esumi et al. [71] arrived at a similar conclusion when studying the adsorption of binary mixtures of cationic surfactants, bis(2-hydroxyethyl) (2-hydroxy-3-perfluorooctylpropyl)methylammonium chloride and hexadecylpyridinium chloride from their solution in water to negatively charged silica. The total adsorption of the mixture was found to be lower than that of single surfactants adsorbed separately, indicating a mutual phobicity between hydrocarbon and fluorocarbon chains. 

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]

Geiry and co-workers [194] found that terminal perfluorination of dode-cyltrimethylammonium bromide reduces solubilization of Orange OT by the surfactant (Fig. 6.37). Because terminal fluorination did not reduce the aggregation number of the micelles substantially, a decrease in micelle size did not appear to be a cause of reduced solubilization. The mutual phobicity between terminal CF3 groups and the hydrocarbon groups of the solubilizate, the dye molecule, was the more likely explanation. Accordingly, fluorinated surfactants are better solubilizers for decafluorobiphenyl than hydrocarbon surfactants [200]. 

Asakawa et al. [202] examined solubilization of octafluoronaphthalene (OFN) and pyrene by anionic surfactants with a fluorocarbon or hydrocarbon hydrophobe and their mixtures. The study confirmed the dependence of solubilization on mutual phobicity between the solubilizate and surfactant chains, as well as the micellar size. The replacement of the lithium counterion with the diethylam-monium counterion increased solubilization of OFN by perfluorononoate and tetradecyl sulfate. The solubilization increase was attributed to an increase in micellar size and counterion binding. The positive effect of micellar size on solubilization was demonstrated by an adding salt (LiCl) or by mixing surfactants. 

The effect of additives on mesophases of fluorinated surfactants has been studied by Tiddy and Wheeler [ 163] and Rosenblatt [176]. Tiddy and Wheeler described the effects of -octanol on the ammonium perfluorooctanoate-water system with a three-component phase diagram (Fig. 7.39). The main differences between phase diagrams for this system and that for sodium octanoate- octanol-water were related to mutual phobicity between fluorocarbon and hydrocarbon chains. Octanol was found to be less soluble in the aqueous micellar phase of ammonium perfluorooctanoate than that of sodium octanoate. However, ammonium perfluorooctanoate is more soluble in octanol than sodium octanoate. This solubility difference is probably related to the effect of counterions, as ammonium salts are usually more soluble in octanol than sodium salts. 

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