Inhibitory effect of sodium carboxymethylcellulose and synergistic biodegradable gemini surfactants as effective inhibitors for MS corrosion in 1 M HCl

The aim of this paper is to study the anticorrosive performance of the polymer-surfactants system comprising of mixed solutions of varying concentrations (10-700 ppm) of sodium salt of carboxymethylcellulose (NaCMC) and fixed concentration (1 ppm) of oppositely charged synthesized green cationic di-ester bonded gemini surfactants i.e., ethane-1,2-diylbis(N,N-dimethyl-N-alkylammoniumacetoxy)dichloride,referred as m-E2-m, where m = 12, 14, 16), respectively for mild steel in 1 M HCl solution. The inhibition effect of mixed NaCMC - gemini surfactant system was examined using weight reduction technique, potentiodynamic polarization (PP) measurements, electrochemical impedance (EIS) measurements, surface morphological observation (SEM), and molecular dynamics simulation study. NaCMC alone was observed to offer moderate inhibition efficiency (IE) of 57.3% at 500 ppm, which was synergistically increased in the presence of very small amount of synthesized gemini surfactants. The improvement in IE was highly dependent on the surfactant tail length; the maximum improvement in IE of 90.1% was observed in presence of 16-E2-16. The adsorption of the studied systems followed Langmuir adsorption isotherm. PP result showed that all the examined systems behave as mixed type inhibitors. EIS results supported the existence of protective layer by the adsorption of inhibitor molecules on the metal surface. The formation of protective layer of studied systems on the mild steel surface was confirmed by FT-IR and SEM results. Molecular dynamics simulation was further performed to provide molecular level insights into the adsorption mechanism with the structure of studied systems. (C) 2019 The Authors. Published by Elsevier B.V.