Fluorocarbon-hydrocarbon hybrid cationic surfactants: Synthesis, surface-activity properties and anti-corrosion performance

Abstract

Fluorocarbon-hydrocarbon hybrid cationic surfactants possess unique performance because they combine the characteristics of fluorocarbon and hydrocarbon surfactants, however, their potential as metal corrosion inhibitors has not been addressed. Here, two hybrid cationic surfactants (F4H6 and F6H6) were synthesized using perfluorobutylsulfonyl and perfluorohexylsulfonyl chains, respectively, through a cationic bridge of N-benzyl-N′,N′-dimethyl ethylenediamine, to connect with a hexyl group as the hydrocarbon chain. Both F4H6 and F6H6 exhibited low critical micelle concentrations as 1.81 × 10−3 and 3.76 × 10−4 M and high aqueous surface activities with surface tensions as low as 22.07 and 18.22 mN/m, respectively. Their anti-corrosion performance for carbon steel in 1.0 M HCl was demonstrated with inhibition efficiencies up to 92.7% and 95.8% at 1.5 × 10−4 M by potentiodynamic polarization, similar to the results obtained by electrochemical impedance spectroscopy. Both surfactants belong to mixed-type inhibitors and adsorbed on carbon steel following the Langmuir isotherm model. Surface analyses by contact angle, SEM, and XPS revealed that F6H6 tended to form an adsorption layer more densely packed than F4H6 on carbon steel, more efficiently preventing corrosive species from corroding the metal. The results proved that such hybrid cationic surfactants can be utilized as promising metal corrosion inhibitors with the potential for wide applications.