Fluorinated surfactants Structures

Partly fluorinated or perfluorinated sulfonic and carboxylic acids are compounds with excellent surface activity combined with an extreme stability against chemical or physico-chemical attacks as also described for non-ionic fluorine containing surfactant compounds. The anionic surfactants are shown with their structural formulae in Fig. 2.11.24(1)—(III). A selected ESI-FIA-MS(-) spectrum of a partly fluorinated surfactant (CF3-(CF2)4-(CH2)8-S03H, m/z 461) is presented in Fig. 2.11.25. The FIA spectrum also contains ions of the by-products CF3-(CF2)2-(CH2)8-S03H (m/z 361) and CF3-(CF2)3-(CH2)8-S03H (m/z 411). 

In this chapter, we focus in two kinds of surfactants that so far have not been common as structure-directing agents in the synthesis of mesoporous silica, namely, silicone and fluorinated surfactants, having a hydrophobic chain different from that of conventional hydrocarbon surfactants, which imparts peculiar properties to the systems. 

Nowadays, partially or fuUy fluorinated surfactants are available with a variety of chemical structure and chain lengths. Therefore hydrophilic-lipophilic properties can be controlled and these new surfactant molecules may provide a rich phase behavior, which could be used to obtain well-organized mesoporous materials. 

Surfactants with hydrophobic chains different from conventional hydrocarbon alkyl chains possess interesting properties as structure-directing agents in self-assembly processes. Both silicone and fluorinated chains are less soluble in many organic solvents than their hydrocarbon counterparts. Moreover, sihcone and fluorinated surfactants reduce the surface tension of water more effectively than... 

Fluorinated surfactants are both hydrophobic and lipophobic. For example, potassium per-fluorooctanesulfonate—an industrially important surfactant —forms a third phase with octanol and water, and it is impossible to determine its octanol-water partition coefficient. " Similar to fluorocarbon-hydrocarbon bulk solvent mixtures, mixed binary systems containing a perfluorocarbon surfactant and a structurally related hydrocarbon surfactant are known to behave nonideally, that is, exhibit phase separation in insoluble monolayers at the air-water interface or form two types of micelles simnltaneously in solution—one type is fluorocarbon-rich and the other is hydrocarbon-rich. This nonideal behavior of fluorocarbon-hydrocarbon surfactant mixtures is used in firefighting foams and powders—an important technical application of fluorinated surfactants. " ... 

VDF and suitable comonomers can be polymerized as a microemulsion where fluorinated oil-in-water microemulsion and fluorinated surfactant are present (37-39). The core-shell structure of these self-assembling systems and their distinctive pol5unerization features along with the range of particle size distribution have been reported (40). 

Details of the processes used to produce vinylidene fluoride-hexafluoropropylene copolymers have not been disclosed but the copolymers may be prepared by emulsion polymerization under pressure using a persulphate-bisulphite initiator system. Highly fluorinated surfactants, such as ammonium perfluorooctoate, are most commonly used in order to avoid chain transfer reactions. The preferred vinylidene fluoride content for commercial copolymers is about 70% mole. The structure of such a copolymer might be represented as follows ... 

In the section that follows, we will address in some detail the stability of anulsions against coalescence and discuss the experimental results within the framework of the structural-mechanical barrier. We will devote special attention to systems with lluorinated interfaces. The most noteworthy result was that the most effective stabilizers for fluorinated hydrocarbons in aqueous solutions were nonfluorinated surfactants, while fluorinated surfactants were very effective for stabilizing emulsions of nonfluorinated hydrocarbons. 

Rosen [35] has tabulated values of Tm for a wide variety of anionic, cationic, non-ionic and zwitterionic surfactants and has discussed the effect of surfactant structure on With hydrocarbon surfactants, the length of the hydrophobic group has little effect except when this exceeds 16 carbon atoms when a significant decrease in r jis noted, possibly due to coiling of the chain. Chain branching has only a small effect on T j, as has introduction of fluorine atoms into the hydrophobic chain. With polyoxyethylene non-ionic surfactants of fixed oxy-ethylene chain length the value of appears to be little influenced by the length of the hydrocarbon chain. 

Surfactant assemblies are generally utilized as a template to form mesoporous shell. Vesicle-like hollow sihca particles can be prepared by sol-gel reactions in the presence of surfactants. Although most of the materials reported so far have multilamellar structures, hollow mesoporous silica particles with a single-walled vesicle structure have been prepared by the reaction of TEOS in the presence of a fluorinated surfactant (lH,lH,2//,2//-perfluorodecylpyridinium chloride). With... 

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