Self-assembled monolayers (SAMs) have attracted considerable interest for surface modification of metals due to their ability to tailor interfacial properties, enhance corrosion resistance, and improve hydrophobicity. In thepresent work, the aging process of octadecanethiol (ODT) SAMs was studied in a wide range of concentration (1,10 and 100 mM) in 3.5 wt% NaCl. The aging process of ODT-SAMs was studied by different electrochemical methods: potentiodynamic dynamic polarization, linear polarization resistance, and lectrochemical impedance spectroscopy. The experimental findings demonstrated that the SAM prepared using 100 mM ODT exhibited perfect corrosion inhibition performance. Specifically, after 1 h exposure to NaCl solution, the SAM exhibited superior corrosion inhibition (99.8%). During 48 h immersion, the polarization resistance (Rp) for all ODT-SAMs initially increases, then decreases, and finally stabilizes at a constant value. The atomic force microscope analysis revealed a positive correlation between ODT concentration and surface characteristics. Specifically, both surface roughness and coverage increased as ODT concentration rose. Moreover, contact angle measurements demonstrated that higher ODT concentrations led to enhanced hydrophobicity of the ODT-SAMs. Morphological examination was performed using scanning electron microscopy. Fourier-transform infrared analysis confirmed the presence of characteristic functional groups indicating the formation of ODT-SAM on the copper surface. After immersion in NaCl solution, the characteristic bands became intensified, indicating structural disordering of the monolayer. The impedance data facilitated a comprehensive analysis of the SAMs’ key properties. This examination encompassed crucial parameters such as: monolayer thickness, molecular tilt angle and surface coverage. The aging mechanism of ODT-SAMs was well studied by both electrochemical and surface analysis methods.

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