Sodium perfluorooctanoate

The application of the activity of the surfactant has been examined also for the surface tension and adsorption of disodlum alkyl phosphate(6,7), sodium dodecyl sulfate(37), alkyl trimethylammonium bromide(35 ), and sodium perfluorooctanoate(13) solutions. These studies show that the surface tension and theadsorption amount are controlled by the activity of surfactant, irrespective of the added electrolyte concentration. 

Partial or total fluorination has striking effects on the CMC. Thus while perfluorinated compounds have much lower CMCs than the corresponding hydrocarbon surfactants (as an example the CMC is 0.030 M for sodium perfluorooctanoate and 0.38 M for sodium octanoate), partial fluorination increases the CMC. The strong deviation from an ideal behavior is illustrated in Fig. 2.425. A markedly nonideal behavior is also found in mixtures of hydrocarbon and fluorocarbon surfactants26. ... 

SDS sodium dodecyl sulfate HDTC1 hexadecyltrimethylammonium chloride HDTBr hexadecyltrimethylammonium bromide Brij 35 polyoxyethylene (23) lauryl ether DTAC dodecyltrimethylammonium chloride TTAC1 tetradecyltrimethylammonium chloride HDPB hexadecylpyridinium bromide KDC potassium decanoate SPFO sodium perfluorooctanoate KTC potassium tetradecanoate... 

The triplet state decay kinetics of benzophenone has been monitored in fluorinated surfactants (sodium perfluorooctanoate, SPFO) where the surfactant does not quench the triplet40>. In this case, the excited benzophenone cannot react with the surfactant and the excited molecule escapes into the aqueous phase. When increasing amounts of SDS is added to solution, the observed triplet lifetime (by nanosecond transient absorption techniques) decreases indicating that hydrogen abstraction is occurring from the SDS (Fig. 17). 

Another interesting feature of fluorinated surfactants is their ability to greatly reduce the surface tension of water, even at very small concentrations. Some surfactants, such as sodium perfluorooctanoate, can lower the surface tension at 25 °C down to 15 mN m" . It should be pointed out that such low tensions can be achieved with a rather short pefluoalkyl chain, because the perfluoalkyl chains are significantly more hydrophobic than the hydrocarbon alkyl chain with the same number of carbon atoms [46]. A remarkable example is sodium fluorobu-tanoate, with a very short chain length, but still able to form self-aggregates in water [47]. 

Sugihara, G. . Yamamoto, M. Wada, Y. Murata, Y. Ikawa, Y. Mixed Micelle Formation in Aqueous Solutions of Nonyl-N-Methylglucamine with Sodium Perfluorooctanoate at Different Pressures. J. Solution Chem. 1988,17, 225-235. 

Trehalose tetraesters characterised by ID and 2D H and C NMR and ESI-MS as biosurfactants (rather than cryoprotectants) were isolated from a soil strain of Micrococcus luteus. Solubilisation of phenol within mieellar aggregates of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions were investigated by H NMR in D20. The synthesis and properties of non-cytotoxic carboxymethylcellulose-chitosan hydrogels modified with poly(ester-urethane) was reported. 2D NOE NMR gave new insights into the interactions between polyamidoamine dendrimers and different surfactants including SDS and dodecyltrimethylammonium bromide. The ability of a- and (3-CDs to disrupt a surfactant mixed micelle of an equimolar mixture of octyltriethylammonium bromide (OTEAB) and sodium perfluorooctanoate (SPFO) was studied by H and F NMR. The effect of ethanol on the micellization of SDS (anionic... 

Figure 10.3. Mixed CMC values of sodium perfluorooctanoate with sodium decyl sulfate (A)...

Fig. 3 Confocal microscopy images of gel particles composed of a polyelectrolyte (cationically modified hydroxyethyl cellulose (JR-400 ) and two different types of surfactants (cetyltri-methylammonium bromide, CTAB, and sodium perfluorooctanoate, FC7). The resulting gel particles can assume two types of morphologies depending on the surfactant concentration a smooth hollow particle with dense thin gel shell for lower concentrations, and b gel particle with sparse thick shell, and a gel corona for higher concentrations. Reprinted from Lapitsky and Kaler [51]. Copyright (2004), with permission firom Elsevier...

As described above, interactions between oppositely charged surfactants and polyelectrolytes in aqueous solutions can lead to associative phase separation, where the concentrated phase assumes the form of a viscous liquid, gel, liquid crystal or precipitate. This behavior has been exploited to form gel particles, which have been prepared by drop-wise addition of cellulose-based polycation solution (chitosan or-, N,N,N-trimethylammonium derivatized hydroxyethyl-cellulose) to anionic (sodium dodecyl sulfate, sodium perfluorooctanoate) and cationic (cetyltrimethylammonium bromide/sodium perfluorooctanoate) surfactant solutions [76-80]. 

Fluorination of the hydrophobe decreases markedly the surfactant concentration needed for a substantial surface tension reduction. At 1 g/L concentration, sodium octanesulfonate, C8H 7S03Na, lowers the surface tension of water at 20°C to 65 nM/m, but sodium perfluorooctanoate, CgHivSOsNa, at the same concentration lowers surface tension to 32 mN/m [49]. Conventional surfactants with a hydrocarbon-type hydrophobe can lower surface tension to 30-35 mN/m at 0.1% concentration. With fluorinated surfactants, surface tensions below 30 mN/m have been achieved at concentrations as low as 10-100 ppm. With some fluorinated surfactants, only 100-200 ppm of the surfactant is needed to lower surface tension below 20 mN/m [48,50]. 

Motomura et al. [100] measured the interfacial tension of aqueous sodium perfluorooctanoate against hexane as a function of temperature around cnic. The entropy and energy of adsorption were found to be higher for sodium perfluorooctanoate than for dodecylammonium chloride or sodium dodecyl sulfate. The... 

A comparison of the sodium perfluorooctanoate and sodium decyl sulfate interfacial pressures at various interfaces showed striking differences between the relative affinities of the surfactant for various interfaces. Although both surfactants have nearly identical cmc values, their adsorption at low surfactant concentrations differ markedly. The perfluorinated surfactant had a higher affinity for the air-water and perfluorohexane-water interfaces than the nonfluorinated surfactant. However, the latter has a higher affinity for the hexane-water interface (Fig. 4.39). The higher affinity of the nonfluorinated surfactant for the hydrocarbon-water interface has been attributed to a more favorable interaction of the hydrocarbon chains at the hydrocarbon-water interface. 

A keen interest in microemulsions of fluorocarbons in water was kindled by the need for synthetic oxygen earners in blood (see Section 10.4). Gerbacia and Rosano [121] prepared a stable fluorocarbon emulsion using a mixture of fluorinated and hydrocarbon-type nonionic surfactants. The droplet size was not determined, however, and the emulsions were not characterized. Oliveros et al. [122] prepared perfluorinated microemulsions consisting of four components (1) sodium perfluorooctanoate, an anionic fluorinated surfactant (2) 2,2,3,3,4,4,4-heptafluoro-1-butanol (3) perfluorohexane (4) water. The pseudoternary-phase diagram (Fig. 4.40) shows two regions. Mi and Mi, of respective W/0 and OAV microemulsions [122]. These optically transparent microemulsions were characterized by nuclear magnetic resonance spectroscopy. 

Rassing et al. [62] studied kinetics of sodium perfluorooctanoate micellar systems using the ultrasonic relaxation method. They observed a fast relaxation process attributed to a micelle formation. The ultrasonic relaxation times revealed that periodic fluctuations in temperature and pressure caused by the acoustic wave are several magnitudes less than the temperature or pressure perturbations of jump techniques. Rassing et al. [62] suggested that the ultrasonic and jump methods measure different modes of micelle formation whose relaxation times differ by several orders of magnitude. Ultrasonic absorption techniques [69-71 ] have also been used to measure relaxation spectra of sodium perfluorooctanoate and cesium perfluorooctanoate [72,73]. 

Several nonfluorinated ionic surfactants have been found to exhibit a cloud point [110-113]. Recently, Yu and Neuman [113] have observed cloud phenomena in an aqueous system containing sodium perfluorooctanoate with an excess of tetrapropylammonium bromide. 

Fisicaro et al. [124] determined the enthalpy of micellization for sodium perfluorooctanoate from heats of dilution using an LKB flow microcalorimeter. The enthalpy value, 8.70 kJ/mol at 25°C, calculated by using the pseudophase transition model is in good agreement with the enthalphy value calculated by using the Woolley and Burchfield one-step mass action model (see Section 6.2). The value reported by Johnson and Olofson [132], — 6.8kJ/mol at 25 C, for... 

The volume change upon micellization reported for lithium perfluorononanoate by La Mesa and Sesta [85], AV = 18 2 mL/mol, corresponds to the value of 20 mL/mol estimated by Sugihara and Mukerjee for sodium perfluorooctanoate [135]. However, the value of 14.2 mL/mol reported by Johnson and Olofsson [132] for lithium perfluorononanoate is considerably lower than the value obtained by La Mesa and Sesta. The V, / = 21.5 1 mL/mol value estimated for perfluorooctanoic acid [88] is higher than that of its sodium salt and ... 

The cmc values are pressure dependent. Sugihara and Mukeqee [135] measured electrical conductivities of sodium perfluorooctanoate solutions as a function of pressure. The cmc values were found to increase with increasing pressure from 1 atm to 2000 kg/cm and then decrease slightly at higher pressures (Fig. 6.26)... 

Fig. 6.26 Effect of pressure on the cmc of sodium perfluorooctanoate at 30"C, using molality and molarity scales. (From Ref. 135. Reproduced by permission of the American Chemical Society.)...

The pseudophase model (see Section 6.2) for micellar solutions makes it possible to establish a partitioning coefficient for the partitioning of the solubilizate between the aqueous solution and the micellar pseudophase. Treiner et al. [206-208] studied partitioning of alcohols and phenol in an aqueous solution of a fluorinated surfactant or of mixed anionic hydrocarbon and fluorocarbon surfactants. The fluorinated surfactants used in their studies were potassium or sodium perfluorooctanoate and lithium perfluorooctanesulfonate. 

The fraction solubilized, by sodium perfluorooctanoate and the partition coefficient, increase with increasing chain length of the alcohol (Table 6.16) [211]. The increase in solubilization was attributed to the increase in hydrophobicity of the alcohols with increasing chain length. The partition ratio of benzene was found to approximate that of butanol. This unexpected result suggested that the solubilization mechanism, and possibly the site of benzene in the micelle, is different from that of alcohols [211]. 

Table 6.16 Partitioning in Micellar Solutions of Sodium Perfluorooctanoate (0.101/W) and a Mixed Micellar Solution of Sodium Perfluorooctanoate (0.0997A//) and Sodium Decanoate (0.0404/W)...

In sodium perfluorooctanoate In sodium perfluorooctanoate -1- sodium decanoate... 

The partition coefficients in the sodium perfluorooctanoate-sodium decanoate system (Table 6.16) are similar to those of the pure perfluorooctanoate system. For benzene, however, the partition coefficient was higher in the mixed system, suggesting again a different solubilization mechanism. 

The differences in thermodynamic parameters of solubilization between flu-orinated surfactants and their hydrocarbon counterparts have been reviewed [124,214]. Fisicaro et al. [124] pointed out the large discrepancies between partition coefficient values obtained by different techniques pointed out (compare the P values for alkanols in sodium perfluorooctanoate given in Tables 6.15 and 6.16). The limited reproducibility appeared to be related to the nature of the micellar systems studied The equilibrium between different kinds of mixed micelles can easily be perturbed by the procedure used for the determination of partition coefficients and the equilibrium is slowly restored. 

Fig. 6.41 Solubility of gas (moles of gas absorbed in 1000 g of water containing sodium perfluorooctanoate) as a function of surfactant concentration at 25°C. (From Ref. 219. Reproduced by permission of Academic Press.)...

Turro and Lee [16] employed the luminescence method to determine the aggregation number for sodium perfluorooctanoate micelles. The aggregation number calculated from quenching of Ru(bpy)3 phosphorescence was found to be seven. Although this numerical value may be inexact, the aggregation number of perfluorooctanoate micelles is undoubtedly much smaller than that of micelles of corresponding hydrocarbon surfactants. In spite of the small size, sodium perflu-... 

Berr and Jones [35] calculated the aggregation number for sodium perfluorooctanoate to be 28 at 0.12M. The smaller aggregation number of sodium perfluorooctanoate allows the the micelle to remain spherical, whereas ammonium perfluorooctanoate with larger aggregation numbers [56] forms ellipsoidal micelles. 

Fig. 7.6 Critical micelle concentrations for mixtures of sodium perfluorooctanoate with sodium decyl sulfate (A) and sodium laurate (O). Dashed lines represent expected values for Ideal mixing, assuming B = 0.645 [Eq. (6)]. Curves 1, 2, 3, and 4 show expected values for complete demixing of micelles [Eq. (7)]. Curve 1 was calculated for B = 0.53 curves 2, 3, and 4 were calculated assuming B = 0.645. (From Ref. 68. Reproduced by permission of the American Chemical Society.)...

Guo et al. [80] have studied mixtures of sodium perfluorooctanoate (SPFO) with a nonionic, an amphoteric, and a cationic hydrocarbon-type surfactant by NMR and surface tension meaurements ... 

Treiner and co-workers [81] measured partitioning of 1-pentanol to elucidate the micellar composition of two aqueous mixed anionic surfactant solutions (sodium decyl sulfate -I- sodium peifluorooctanoate and sodium dodecyl sulfate + sodium perfluorooctanoate). The partition coefficient exhibited a maximum in hydrocarbon-rich mixtures in both mixed micellar solutions. The synergistic effect was attributed to hydrocarbon-fluorocarbon repulsive interaction and found to be in accord with the regular solution model using interaction parameters determined for binaiy surfactant solutions. 

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