Adipic acid was used to synthesize three nonionic Gemini surfactants containing different numbers of
propylene oxide units in their structures. The produced surfactants have been characterized employing
FTIR and 1H-NMR spectra. Some of the physical properties of them, namely, surface tension, maximum
surface excess concentration, surface pressure, critical micelle concentration, and the minimal area of
the surface taken by a single molecule, were computed. The inhibitory effect of the synthesized
surfactants on the corrosion of C-steel (C45) in 1.0 M HCl solution was studied. Gravimetric and
electrochemical methods were used for corrosion rate measurements. The outcomes acquired from the
used methods showed that every one of the three surfactants works as a strong inhibitor for steel acidic
corrosion. By raising surfactant concentration and exposure time, the inhibition proficiency improves.
The inhibition efficiency exceeded 90% for the three compounds. The higher the propylene oxide units
contained in the surfactant molecule the higher is its inhibition efficiency. Based on the findings,
a mechanism for inhibitory action was proposed. Moreover, the density functional theory (DFT) and
molecular electrostatic potential (MEP) were investigated for the three inhibitors. The calculated parameters were correlated with the inhibition efficiency.