FLUOROSURFACTANTS

ð  Surfactants which contain one or more fluorinated or partially fluorinated hydrophobic groups are called fluorosurfactants or fluorinated surfactants.

ðThey show different properties than those of hydrocarbon surfactants.

ðHowever, like conventional surfactants, fluorosurfactants generally contain a hydrophilic groups and hydrophobic group within the same molecule.

ðThe hydrophobic group of fluorinated or semiflourinated surfactants can be linear or branched and may contain an aromatic group or additional elements as O, N, Cl, S and Si.

ðSome examples are,

C_nF_(2n+1)

C_nF_(2n+1)OC₆H₄^-

C₈H₁₇CH₂CH₂Si(CH₃)₂^-

Classification

            They can be classified according to change type of the hydrophilic groups.

(1) Anionic:-They contain (-)VE charge and so they are sensitive to pH and electrolyte concentration and may precipitate in water containing di- or tri- valent metal ions.

Examples are

Carboxylate           :-          R_fCOO^-M⁺

Sulphonates           :-          R_fSO₃^-M⁺

Sulphates               :-          R_fSO₄^-M⁺

Phospahtes            :-          R_fOP(O)O₂^-M₂⁺  etc.

Where, R_f is fluorinated or semifluorinated hydrophobic parts and M⁺ is an organic or inorganic counterion.        

(2) Cationic:- Like anionic, they are sensitive to pH and electrolyte content. The fluorinated hydrophobic is attached directly to quaternary ammonium group, a protonated group or a heterocyclic base.

(3) Non-ionic:- They include polyoxyethylene and polyoxyalcohols.

Oxyethylated alcohol                    :-          R_fCH₂O(CH₂CH₂O)_mH

Oxyethylatedthiol                         :-          R_fCH₂CH₂S(CH₂CH₂O)_mH

Fluorinated polyhydric alcohol     :-          R_fCH₂CH₂O[CH₂CH(CH₂OH)O]_mH

(4) Zwitter ion:- Over a pH as and their isoelectric point, they have zero overall charge but highly polar. They may function as either anionic or cationic depending upon pH of solution. Examples are,

Carboxybetaines   :-RfCH₂CH(COOCH₃)CH₂N⁺(CH₃)₂^-CH2COO^-

Sulphobetaines, sulphatobetaines etc.

Synthesis

            Most modern method of manufacture, involve reacting tetrafluorinatedethylene with a fluoride ion (Ca, K or tetraalkylammonium fluoride) in polar solvents (eg. DMF).

Polymerisation takes place and pentamer is used for further synthesis. This pentamer is coupled with phenol.

This phenol group can be sulphonated to give an anionic detergent.

    ðIt may be chlorosulphonated to give sulphonyl chloride, then treated with N,N’-dimethyl propane diamine, to give a tertiary amine and then quaternised with methyl iodide to give a cationic detergent 

 ðThe tertiary amine can also be reacted with propiolactone to produce an amphoteric surfactants.

Properties:- The unique properties are

ð  They have the surface tension of aqueous system to 2.0 N/m²

ð  They are effective even in the concentration of the order of 0.01 %.

ð  They show surface activity in organic system.

ð   They are chemically stable.

Applications

ð  They have excellent wetting properties.

ð  A fluorosurfactant treatment can make the textile resistant to wetting and penetration by both water and oil.

ð  They are used in emulsion polymerisation of fluoropolymer.