Terminally fluorinated surfactants

L phase materials formed by combining a conventional RTIL with an amphiphilic LC mesogen has been found to have ca. three orders of magnitude higher ionic conductivity parallel vs. perpendicular to the lamellae [88]. Similar anisotropic ion conductivity results have also been obtained with L phases of imidazolium-based amphiphiles and also hydroxyl-terminated fluorinated surfactants formed by mixing with imidazolium-based RTILs (Fig. 12) [89,90]. 

Partially fluorinated surfactants also have been investigated by NMR. Muller and Birkhahn [27] found the fluorine chemical shift for anionic terminally fluorinated surfactants, CF3(CH2)sCOONa and CF3(CH2)ioCOONa, to be essentially independent of ionic strength. An added electrolyte depressed cmc but did not affect the chemical shifts for the surfactant anions in the micelle. They explained their results by the formation of prolate-shaped spheroid micelles in the presence of sufficient electrolyte. An alternative explanation that electrolytes do not increase the micellar size was considered to be unlikely. 

Despite the fact that physico-chemical and chemical degradations were not possible, the isolation of persistent metabolites of the CnF2n+i-(CH2-CH2-0)m-H compound generated by (3 and w oxidations of the terminal PEG unit of the non-ionic blend was reported, but environmental data about this type of compound are still quite rare [49]. TSI(+) ionisation results of the industrial blend Fluowet OTN have been reported in the literature [7,51]. Actual data of non-ionic fluorinated surfactants were applied using ESI- and APCI-FIA-MS(+) and -MS-MS(+), which reported the biodegradation of the non-ionic partly fluorinated alkyl ethoxylate compounds C F2 fi-(CH2-CH2-0)x-H in a lab-scale wastewater treatment process. 

The free-radical addition of TFE to pentafluoroethyl iodide yields a mixture of perfluoroalkyl iodides with even-numbered fluorinated carbon chains. This is the process used to commercially manufacture the initial raw material for the fluorotelomer -based family of fluorinated substances (Fig. 3) [2, 17]. Telomeri-zation may also be used to make terminal iso- or methyl branched and/or odd number fluorinated carbon perfluoroalkyl iodides as well [2]. The process of TFE telomerization can be manipulated by controlling the process variables, reactant ratios, catalysts, etc. to obtain the desired mixture of perfluoroalkyl iodides, which can be further purified by distillation. While perfluoroalkyl iodides can be directly hydrolyzed to perfluoroalkyl carboxylate salts [29, 30], the addition of ethylene gives a more versatile synthesis intermediate, fluorotelomer iodides. These primary alkyl iodides can be transformed to alcohols, sulfonyl chlorides, olefins, thiols, (meth)acrylates, and from these into many types of fluorinated surfactants [3] (Fig. 3). The fluorotelomer-based fluorinated surfactants range includes noiuonics, anionics, cationics, amphoterics, and polymeric amphophiles. 

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. 

Branching of the fluorocarbon chain decreases the efficiency of a fluorinated surfactant in surface tension reduction [57,58]. In analogy, a condensed (spread) monolayer of a perfluorinated n-alkanoic acid has a lower critical surface tension than its terminally branched isomer. Bemett and Zisman [59] attributed the effect of branching to different molecular packing and carbon chain adlineation. 

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]. 

The fluorine NMR chemical shifts of terminally fluorinated cationic surfactants 12,12,12-trifluorododecyltrimethylammonium bromide and 10,10,10-tri-fluorodecyltrimetylammonium bromide are similar to those of the corresponding anionic and nonionic surfactants with a terminal trifluoromethyl group [32]. When the counterion is fluoride, instead of bromide, the chemical shift of the fluoride counterion is concentration dependent. The trifluoromethyl chemical shifts were interpreted utilizing a double-equilibrium model. The aggregation number was estimated to be 25 in dilute solutions from the curvature of the chemical shift concentration plots near the first cmc. Above the second cmc, the aggregation number was assumed to be 60, considered the spatial limit for 12-carbon surfactant chains in a spherical micelle. 

The pseudophase separation model of micellar solutions considers a micelle to be a pseudophase in a liquid state. Because the micelles are assumed to have a liquidlike core, the mutual solubility of a fluorinated surfactant and a hydrocarbon surfactant in mixed micelles is, according to the pseudophase model, governed by the miscibility of the fluorocarbon and hydrocarbon chain. For example, heptane and perfluoroheptane are immiscible at 25°C, but above 50°C, these liquids are miscible in all proportions [75]. A terminal substitution of a hydrophilic group depresses the enthalpy of mixing and makes the components miscible at 25°C. 

Methyl ation of the terminal hydroxyl in nonionic fluorinated surfactants has only a slight effect on the phases formed in water at low temperatures [181]. At temperatures above about 30-40°C, none of the isotropic and anisotropic phases can exist and no stable bilayer structures can be formed. Although the temperature range of the phases is reduced by capping of the terminal hydroxyl, the sequence of the phases does not change. 

A perfluorinated surfactant will have all carbon-hydrogen bonds replaced by carbon-fluorine, so that the simplest formula for the saturated materials will be CF3(C F2 )S, where S signifies any of the possible surfactant head groups. Since various degrees of branching along the fluorocarbon chain are common, especially in commercial samples, care must be taken in the evaluation of such materials and the interpretation of experimental results. If hydrogen is substituted for a terminal fluorine, there will be a increase in the cmc and the minimum surface tension the surfactant can produce in aqueous solution (Table 4.14). 

Linear alkylbenzenes are made from linear terminal olefins and benzene and are important precursors of biodegradable anionic surfactants (LAS, linear alkylbenzenesulfonates). The conventional catalyst is HF, first to be replaced by a fluorinated silica-alumina in the DETAL process. The DETAL process is safer than the HF process and also more cost-effective because no special metallurgy is required and no calcium fluoride waste stream exists.52 Zeolites such as Beta may come to the fore here because they display a higher selectivity to the desired 2-phenyl isomers.55... 

The same team has also described the selective hydrogenation of cis-2-pentenenitrile with surfactant-stabiUzed ammonium perfluorotetradecanoate bimetallic Pd-Ru nanopartides prepared via in situ reduction of their simple salts in reverse micelles in SCCO2 [22]. The optimized ratio Pd Ru nanopartide (1 1) shows the highest activity for the hydrogenation of functionalised alkene under mild conditions. No hydrogenation of the terminal nitrile of the molecule in amine was observed and, finally, this fluorinated micelle-hosted bimetallic catalyst gives relevant activity and selectivity in the supercritical fluid without deactivation for at least three catalytic cycles. 

The first use of NMR methods to study polymer/surfactant interaction was by Muller and Johnson (47), who studied the NMR shift (5) of the fluorine atom in PEO/F3 SDS mixtures and obtained results in harmony with the foregoing (F3 SDS is a modification of SDS in which the terminal CH3 group is replaced by CF3). Thus, in the presence of PEO (constant amount) at a certain concentration (Tj) of added F3 SDS, lower than its c.m.c., a slope change in the 8 versus reciprocal concentration plot was observed. At a second concentration T2), above the c.m.c., the slope changed again to a value close to that observed in polymer-fi-ee micellar F3 SDS solutions. Tj was found to be independent of polymer concentration while T2, again, increased with it. 

The effect on micellar properties of the introduction of a fluorine atom into the hydrocarbon chain has been investigated. Muller et al [24-27] reported that substitution of the CF3 group for the terminal CH3 group of the surfactants... 

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