Nonionic fluorinated surfactant system

Viscoelastic Worm-Like Micelles in Nonionic Fluorinated Surfactant Systems... 

In this chapter, a brief theoretical background on the rheological behavior of viscoelashc worm-like micelles is given. It is followed by a discussion on the temperature-induced viscosity growth in a water-surfactant binary system of a nonionic fluorinated surfactant at various concentrations. Finally, some recent results on the formation of viscoelastic worm-like micelles in mixed nonionic fluorinated surfactants in an aqueous system are presented. 

Antonietti et al. described the preparation of mesoporous silica in systems containing mixtures of nonionic fluorinated surfactants and nonionic hydrocarbon block copolymer surfactants [60], The fluorinated surfactant was CF3(CF2)6-i6 C2H4(E0)4 5 and the hydrocarbon-based copolymer was poly(ethylene-co-bulylene)-block-poly(ethylene oxide). 

FLUORAD fluorochemical surfactant PC-170C is a general purpose nonionic fluorinated surfactant which is characterized by its ability to contribute excellent wetting, spreading and leveling properties to a variety of systems, often with a minimum of foaming. 

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]. 

Robert and Tondre [127] studied reverse microemulsions consisting of water emulsified in a binary mixture of a fluorocarbon and a nonionic fluorinated surfactant. Surfactants of the structure C6Fi3CH2(OC2H4) OH, with n = 4, 5, or 6, emulsified large amounts of water (up to 20 wt% water in perfluorodecalin) in fluorocarbons. The solubilization of water by nonionic fluorinated surfactants in fluorocarbons follows the same trends exhibited by hydrocarbon-type systems. 

The foaming properties of fluorinated surfactants vary widely (see Section 4.9). For example, amphoteric surfactants, Zonyl FSK and Zonyl FSC, are outstanding foaming agents. In contrast, the anionic fluorinated surfactant, Zonyl FSP, and the nonionic fluorinated surfactant, Zonyl FSN, are low foaming. In some systems, Zonyl FSP can function as an antifoam agent. 

Fluorinated surfactants are available as liquids, pastes, or solids. Some are diluted with water or an organic solvent some are sold in the 100% active ingredient form. If the system cannot tolerate water, an undiluted fluorinated surfactant or a surfactant formulated as an organic solution has to be used. Some nonionic fluorinated surfactants, (e.g., Fluorad FC-430, Zonyl FSN-100, and Zonyl FSO-100) are soluble in several nonaqueous solvents. Generally, the surfactant must be soluble to be effective. Hence, solubility of the surfactant may limit its use in some systems. 

Ravey and Stebe [223,224] studied SANS of nonionic fluorinated surfactant gels. SANS spectra of systems containing a fluorocarbon, nonionic fluorinated surfactant, and large amounts of water were interpreted in terms of water-in-(water-in-oil microemulsions) emulsions. 

Because most fluorinated surfactants are commercial products containing several components, the toxicity of impurities in fluorinated surfactants has to be considered. Commercial fluorinated surfactants are usually sold as solutions in an aqueous solvent [10]. In some cases, the solvent may cause more systemic or local toxic effects than the surfactant itself. The solvent and volatile impurities may dominate the toxic effects produced by inhalation. Nonionic surfactants with a poly(oxyethylene) hydrophilic chain may contain 1,4-dioxane, which has shown carcinogenic activity in some animal tests. 1,4-Dioxane is a by-product found in nonionic surfactants, regardless of whether the surfactants are fluorinated. However, the concentration of 1,4-dioxane in nonionic surfactants is carefully controlled and is usually very low (about 0.1% or less). Air monitoring has indicated that at a workplace where there are nonionic fluorinated surfactants containing about 0.1 % dioxane, the 1,4-dioxane concentration in air would be below 1 ppm. 

The adsorption of fluorinated surfactants at the electrode-solution boundary is of considerable practical interest for the application in electrochemical systems [60-64) (see Chapter 8). The electrochemical behavior of Zonyl FSN (nonionic), Zonyl FSD (cationic), Zonyl FSA (anionic), Fluorad FC-99 (anionic), and Fluorad FC-135 (cationic) at Hg and Pt electrodes has been investigated by using cyclic voltammetry and interfacial differential capacitance measurements. When the electrode is relatively hydrophobic, such as Hg, and the surface charge density is relatively low, the fluorinated surfactants, as well as hydrocarbon surfactants, are adsorbed with their hydrophobic segments oriented toward the electrode. The interaction of fluorinated surfactants with the Hg electrode is weaker and the adsorbed layer is less compact than those of hydrocarbon surfactants. When the electrode is more hydrophilic, such as Pt, or the surface charge density is high, the surfactants adsorb with their hydrophilic end group toward the electrode surface. 

The anionic fluorinated surfactant (SPFO) forms with the nonionic or the amphoteric hydrocarbon surfactant mixed micelles containing both types of surfactants. Both systems exhibit a negative deviation from ideality. Changes of the F and H chemical shifts of the two surfactants upon mixing are consistent with pseudophase diagrams, calculated from the cmc dependence on the fluorinated surfactant mole fraction. The interpretation of data was based a modified regular solution theory and the phase-separation model. 

Research on the micelle structure and interactions of fluorinated surfactants is ongoing with the main focus on mixed-surfactant systems. Mixtures of fluorinated and nonfluorinated surfactants may consist of anionic, nonionic, or cationic components. Most of the systems investigated so far have contained a fluorinated anionic surfactant and an anionic hydrocarbon surfactant. Anionic fluorinated surfactant mixtures with nonionic or cationic hydrocarbon-type surfactants have been investigated as well. The nonionic fluorinated hydrocarbon surfactant mixtures and cationic fluorinated hydrocarbon surfactant mixtures have been the subject of only a few studies. 

Abe et al. [124] have studied mixed-surfactant systems consisting of a nonionic hydrocarbon surfactant [Ci6H330(C2H40)2oH] and an anionic fluori-nated surfactant (ammonium perfluorooctanoate or ammonium perfluorode-canoate). Dynamic and static light-scattering and fluorescence probe measurements revealed mixed-micelle formation. Penetration of the anionic fluorinated... 

Defoamers for fluorinated surfactants Fluorad FC-129 (anionic), FC-135 (cationic), and FC-170C (nonionic) in aqueous media and Fluorad FC-430 (nonionic) in aqueous and organic solvent media were evaluated by defoamer manufacturers and the 3M Company. The list of effective defoamers compiled by 3M recommends different defoamers for each of the fluorinated surfactant tested. Because the effectiveness of the defoamer depends on the medium as well, a recommended defoamer must be tested for suitability in the coating system used [8]. 

---