General Properties of Fluorinated Surfactants

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]. 

Partially fluorinated surfactants have several advantages with respect to their per-fluorinated counterparts, due to the low solubility of fuUy fluorinated chains in hydrocarbons. The hydrocarbon segment of a partially fluorinated surfactant provides solubility in commonly used organic solvents, lowers the melting point of the surfactant, reduces volatility and decreases the acid strength of perfluorinated acids [51]. 

Fluorinated surfactants can be very intereshng for the preparation of mesoporous materials, due to their good self-aggregation properties, allowing a more precise control of the mesostructure and properties of materials. In this context, the use of fluorocarbon surfactants allows the formahon of ordered mesoporous materials with a long-range organizahon [52, 53], 

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. 

The use of fluorinated surfactants, in the preparation of mesoporous materials will be described in the following section. 

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