Abstract
Alkylphosphonic acids are well known for their ability to form self-assembled monolayers on hydroxide surfaces. A crucial step to understanding fundamentally how these surfaces are created is the elucidation of the interaction process that leads to such interface creation. In this study, we employed electrochemical impedance spectroscopy (EIS), Monte Carlo and molecular dynamics to understand this process. The interaction with the Cu(111) surface of three different alkylphosphonic acids (hexyl-, octyl- and decylphosphonic acids) is evaluated in an aqueous acidic and in an ethanol solution by Monte Carlo and molecular dynamics simulations, while EIS measurements are used to put in evidence the impact of the layer made in ethanol on copper protection. Nyquist diagrams of copper samples modified with an alkylphosphonic monolayer showed a higher polarization resistance that mitigates the copper corrosion in an aqueous acid medium. The phase–frequency Bode plots had higher and broader phase maxima for a modified copper surface with phosphonic moieties, which confirmed the ability of this organic layer to prevent copper corrosion.
Highlights
The electrochemical impedance spectroscopy (EIS) results showed that all three alkylphosphonic self-assembling layers (SAM) on a copper surface had a much higher diameter of capacitive loop in the high frequency region (-Z” values: 4200, 6500 and 5000 Ω) than the 300 Ω of the bare Cu electrode
Almost all samples showed a straight line at low frequencies that was attributed to the diffusion of dissolved oxygen to the unmodified or modified copper surface [38,39]
The EIS results of the adsorption of phosphonic acids onto a copper (111) surface showed very good metal corrosion protection with an inhibition efficiency up to 95%
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Inorganic compounds such as chromate (CrO4 2− ) have been used for many purposes such as chrome plating, leather tanning, copy machine toner, etc. Chromic anodizing has been applied for a long time in the aerospace industry due to its ability to protect aluminum alloys with copper (AA2000) against corrosion and to improve paint adhesion on their surfaces. Molybdate (MoO4 2− ) ions have shown protection abilities against zinc and copper [2,3] corrosion in the presence of chloride ions and copper and mild steel corrosion in artificial sea water [4]
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