Cationic–anionic fluorinated surfactant mixtures based on short fluorocarbon chains as potential aqueous film-forming foam
A strategy for aqueous film-forming foam (AFFF) using cationic-anionic surfactant mixtures with short fluorocarbon chains (≤C4) in both cationic and anionic surfactants was proposed. The minimum surface tension (γmin) of mixtures of C4F9SO2NH(CH2)3N(CH3)3I (C4FI) and CnF2n+1COONa (n = 1, 2, 3, 4) with different molar ratios (5:1, 2:1, 1:1, 1:2, 1:5) was measured at 25 °C. The γmin for all mixtures of C4FI–CnF2n+1COONa were remarkably lower than that of pure C4FI. Among these mixtures, the equimolar mixture of C4FI–C3F7COONa was chosen because of the low γmin, qualified solubility and relatively high fluorine efficiency. The spreading coefficients of its aqueous solution on n-heptane, toluene, benzene, cyclohexane and gasoline were all positive, indicative of its potential in AFFF. The film spreading, sealability and foaming were also tested. The influences of ‘green’ additives (alkyl glucose amide, xanthan gum and sodium carboxymethylcellulose) on foaming performance were studied, in which small dosage of xanthan gum could greatly retard the drainage of foam. It was confirmed that the mixing of oppositely charged surfactants both possessing short fluorocarbon chains was a valuable thought to design AFFF. In application, the quaternary ammonium surfactant likewise can be bromide or chloride rather than iodide for reasons of cost-reduction and stability.
