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Adsorption of fluorinated surfactants

The unequal adsorption to the liquid-vapor and solid-liquid interfaces has been the subject of several studies [34,36,38]. In contrast to Bemett and Zisman [33], Pyter et al. [34] explained the different wetting characteristics of hydrocarbon surfactants and fluorinated surfactants by low adsorption of fluorinated surfactants on nonpolar solids. The higher contact angles exhibited by solutions of fluorinated surfactants on polyethylene were explained by poor adsorption of fluorinated surfactants instead of the strong adsorption proposed by Bemett and Zisman [33]. [Pg.183]

The adsorption of fluorinated surfactants on coal was investigated by Lai and Gray [52] by measuring the contact angles, the spreading coefficient, and the effect of the fluorinated surfactant on flotation. The fluorinated surfactants used were Zonyl FSN (nonionic), Zonyl FSC (cationic), Zonyl FSK (amphoteric), and Zonyl FSA (anionic). The contact angle of water on coal is about 38°-42°. The anionic fluorinated surfactant increased the contact angle to 80°-90°. The other fluorinated surfactants were less effective. The adsorption of the fluorinated surfac-... [Pg.187]

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. [Pg.189]

Although much progess has been made, more fundamental information on the adsorption of fluorinated surfactants on solid surfaces is needed. Because most commercial applications involve surfactant interactions at the solid-liquid boundary, the adsorption phenomena are of great practical interest. Fluorinated surfactants are usually mixtures of homologs and are frequently employed as mixtures with hydrocarbon surfactants. Therefore, a thorough understanding of adsorption mechanisms for surfactant mixtures on solid substrates is also very important (see Section 5.2). [Pg.189]

Fluorinated siufactants have been evaluated for paper uses since die early 1960s [13, 95, 96]. Perfiuorooctyl sulfonamido ethanol-based phosphates were the first substances used to provide grease repellence to food contact papers [97-99]. Fluorotelomer thiol-based phosphates and polymers followed [100-102]. Since paper fibers and phosphate-based fluorinated surfactants are both anionic, cationic bridge molecules need to be used in order to ensure the electrostatic adsorption of the surfactant onto the paper fiber. These surfactants are added to paper through the wet end press where cellulosic fibers are mixed with paper additives before entering the paper forming table of a paper machine. This treatment provides excellent... [Pg.17]

Clayfield et al. [48] attempted to prepare monolayers of fluorinated surfactants FC134 and FX161 on glass by adsorption from acetone solutions. Stable and reproducible contact angles were obtained with n-alkanes, but polar liquids such as water caused desorption of the surfactant from the solid-liquid interface. [Pg.187]

Adsorption of binary surfactant mixtures at a solid-solution interface has been exploited commercially in many applications. In spite of the widespread use of hydrocarbon surfactant-fluorinated surfactant mixtures, very few articles have been published on their adsorption at a solid-solution interface. [Pg.190]

The Upophobicity of fluorinated surfactants also may contribute to their toxicity. It is plausible that the lipophobicity of fluorinated surfactants in conjunction with a high surface activity and consequent strong adsorption may interfere with normal functioning of cells. [Pg.453]

Fluorinated surfactants have unique properties and are therefore indispensable. A potential effect on the environment can be reduced by (1) using synergism with hydrocarbon-type surfactants to minimize the concentration of fluorinated surfactant where feasible and (2) removing fluorinated surfactants from wastewater at industrial sites by adsorption or converting the surfactant by partial biodegradation to physiologically inert substances. [Pg.461]

FIG. 5 Adsorption isotherms of fluorinated surfactants obtained by neutron reflectivity and tensiometry measurements (a) di-CF4, (b) di-HCF4, and (c) di-FICF4GLU. Example error bars are shown for some points. (From Ref. 44.)... [Pg.313]

Downer A, Eastoe J, Pitt AR, Penfold J, Heenan RK. Adsorption and micelli-sation of partially- and fully-fluorinated surfactants. Colloids Surf A Physico-chem Eng Aspects 1999 156 33-48. [Pg.23]

Thus, for example, in the presence of some highly fluorinated carboxylic acids and their salts, the value yc for polyethylene is decreased from its usual value of almost 31 mN/m to about 20 mN/m (Bernett, 1959) by adsorption of the fluorinated surfactants onto the polyethylene surface, with the result that solutions of these surfactants having surface tensions less than the normal yc for polyethylene do not spread on it. The requirement that the surface tension of the wetting liquid be reduced by the surfactant to some critical value characteristic of the substrate is thus a necessary, but not sufficient, condition for complete spreading wetting. A surfactant solution whose surface tension is above the critical tension for the substrate does not produce complete wetting, but a solution whose surface tension is below the critical tension for the substrate may or may not produce complete wetting (Schwarz, 1964). [Pg.257]

These tables indicate that in the presence of Pluronic surfactant the strength of the adsorption layer at the interface between fluorinated phases and water was two orders of magnitude higher than the strength of the layer formed by the same surfactant at the water-heptane interface. In the case of an adsorption layer formed with the fluorinated surfactant, the opposite effect was observed the strength of this adsorption layer at the water/heptane interface was an order of magnitude higher than that of an adsorption layer formed at the fluorinated hydrocarbon/water interface. [Pg.123]

M. Eguchi, S. Takagi, H. Tachibana, H. Inoue, Adsorption of gasous molecule within poly-fluorinated surfactant/saponite hybrid compound, J. Phys. Chem. Solids, 65, 403-407 (2004). [Pg.488]

Downer et al. [29,30] used neutron reflection and surface tension measurements to investigate the adsorption of four fluorinated surfactants at the air-water interface. The surfactants used were two single-chain carboxylates, sodium per-fluorononanoate (NaPFN) and sodium 9H-perfluorononanoate, and two doublechain sulfosuccinates, sodium bis(l/ir, lH-perfluoropentyl)-2-sulfosuccinate (DCF4) and sodium bis(lH, IH, 5H, 5/f-octafluoropentyl)-2-sulfosuccinate (DHCF4). The replacement of a terminal fluorine by hydrogen creates a permanent dipole in the hydrophobic chain and consequently, increases the cmc and the limiting surface tension as well. [Pg.109]

For practical purposes, it is not only important to know how much of a fluorinated surfactant is needed to reduce surface tension to a desired value. The time required to decrease surface tension is also highly significant. Many industrial processes do not allow sufficient time for a surfactant to attain equilibrium and depend on the kinetics of surfactant adsorption. [Pg.133]

Batts and Paul [101b] used time-of-flight secondary-ion mass spectrometry (ToF-SIMS) to investigate the competitive adsorption of a cationic fluorinated surfactant (FC-134) at the gelatin-air interface. ToF-SIMS is a very sensitive surface analysis technique. In the static mode, the sampling depth of ToF-SIMS is only one to two monolayers. However, the ToF-SIMS data are difficult to interpret in quantitative terms and experimental conditions must be carefully controlled. Batts and Paul used positive secondary-ion spectra only, although negative-ion spectra may have been used as well. [Pg.405]


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See also in sourсe #XX -- [ Pg.313 ]




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