Gemini surfactants of the type 1,2-ethanediyl bis-(dimethylalkylammonium bromide)

Gemini surfactants in the series 1,2-ethanediyl bis-(dimethyl-alkylammonium bromide), referred to as (n-2-n), were synthesized, purified and characterized by elemental analysis, 1H NMR, 13C and mass spectra. The thermodynamic properties of aqueous solutions of these surfactants were studied by different techniques. Thus, for gemini (10-2-10), cryoscopic osmometry was used to determine the c.m.c. and osmotic coefficient. By density measurement, the c.m.c., molar volume at the c.m.c. and the volume change during micellization were determined. Gemini (10-2-10) and higher homologs (12-2-12) and (14-2-14) were also investigated by electrical conductivity and surface tension measurements. Electrical conductivity measurements were used to determine their c.m.c. and degree of ionization. From surface tension versus log (molar concentration), we determined the c.m.c., surface tension at the c.m.c. (γc.m.c.), pC20 (negative log of the surfactant's molar concentration, C20, required to reduce the surface tension by 20 mN/m). The surface excess (Γmax) at the air/aqueous solution interface, the minimum area per surfactant molecule at the air/aqueous solution interface (A0) and the critical packing parameter (CPP) were then calculated. Surface tension measurements show that while the alkyl chain affects the critical micellar concentration it has little effect on the area per molecule at the air/water interface. The inhibitive effect of these compounds on the corrosion of iron in hydrochloric acid was also studied using gravimetric and electrochemical impedance spectroscopy. The results obtained show that these compounds are good inhibitors of iron corrosion and reach their maximum inhibition efficiency near their critical micellar concentration.Peer reviewe

Synthesis of some cationic gemini surfactants and their inhibitive effect on iron corrosion in hydrochloric acid medium

Some gemini surfactants in the series of 1,2-ethane bis(dimethyl alkyl (CnH2n+1) ammonium bromide) referred as n-2-n have been synthesized, where n = 10, 12 and 14. The purity of surfactants synthesized was checked by rutinary methodologies (1H-NMR, MS and elemental analysis). Their surface active properties at equilibrium in water at 25 °C were determined. The inhibitive effect of these compounds, in the case of iron immersed in 1 M HCl, was investigated through mass-loss, potentiokinetic methods and electrochemical impedance spectroscopy. Polarization data indicate that these compounds act as very good cathodic inhibitors of iron in 1 M HCl. In the anodic range, the surfactants studied do not show an inhibition effect at iron electrode potential more positive than -100 mV/Saturated Calomel Electrode. Impedance plots of iron in the presence of various concentrations of surfactants studied are similar to semicircles in the capacitive quadrant. The associated values of transfer resistances increase by increasing the additive concentrations. From all measurements performed, the variation of the inhibition efficiency versus concentration shows the same trend. The gemini surfactants appear to be adsorbed in the metal/liquid interface through the general adsorption mode following the Frumkin adsorption isotherm model. The electrochemical impedance spectroscopy shows that the maximum inhibition efficiency is attributed to a formation of an adsorbed layer at the iron surface. From tensiometric measurements, it was found that the ability of gemini surfactants studied to adsorb at the interface air/water is concordant with their order of the inhibition efficiency of iron corrosion.We thank the CNPRST for its financial support (PARS Chim.008) and the TWAS (Grant 97-121 RG/CHE/AF/AC).Peer reviewe

Corrosion inhibition of iron in 1 M HCl by some gemini surfactants in the series of alkanediyl-α,ω-bis-(dimethyl tetradecyl ammonium bromide)

Three new gemini surfactants in the series of alkanediyl-α,ω-bis-(dimethylalkyl ammonium bromide) were synthesised and tested as corrosion inhibitors of iron in hydrochloric acid medium using gravimetric, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) measurements. Results obtained show that the surfactants studied are good cathodic inhibitors and act on the cathodic hydrogen reaction without modifying its mechanism. EIS results show that the changes in the impedance parameters (RT and Cdl) with concentration of surfactants studied is indicative of the adsorption of molecules of surfactant leading to the formation of a protective layer on the surface of iron. The effect of the temperature on the iron corrosion in both 1M HCl and 1M HCl with addition of various concentrations of 1,2-ethane bis-(dimethyl tetradecyl ammonium bromide) in the range of temperature 20-60°C was studied. The associated apparent activation corrosion energy has been determined.We thank the CNPRST for its financial support (PARS Chim.008) and the TWAS for its Research Grant: 97-121 RG/CHE/AF/AC.Peer reviewe