Streamlined approach for covalently anchoring end-functionalised cationic monolayers onto silver substrates for surface coatings

The successful fabrication of high-quality, functionalised monolayers demands a meticulous understanding of the intricate interplay between solvent properties and deposition time. This study introduces a streamlined method for covalently anchoring end-functionalised cationic self-assembled monolayers (SAMs) onto silver (Ag) substrates, achieving enhanced surface coverage, uniformity, and electrochemical performance. The ammonium-terminated SAM, dibromo-10,10’-bis(triethylammoniumdecyl)disulfide (C10-TEA-SAM), was synthesised and its structure confirmed via ¹H NMR spectroscopy. Optimised C10-TEA-SAM immobilisation onto Ag surfaces, employing ethanol as the solvent due to its superior solvating ability for the ionic C10-TEA-SAM molecules, yielded a well-covered, hydrophilic surface. Contact angle (CA) measurements revealed a progressive decrease in CA with increasing immersion time, reaching a minimum of 5.85° after 5 days, indicative of enhanced hydrophilicity. Furthermore, atomic force microscopy revealed a concomitant reduction in surface roughness with prolonged immersion, suggesting the formation of a smoother and more uniform monolayer. Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy confirmed the presence of the C10-TEA-SAM on the Ag surface, while electrochemical impedance spectroscopy (EIS) revealed the insulating nature of the Ag/C10-TEA-SAM interface. This insulating behaviour, characterised by a larger semi-circle impedance and increased bulk resistance, is indicative of a highly ordered, defect-free structure with minimal electron transfer, analogous to long-chain alkanethiol monolayers. These findings collectively demonstrate the efficacy of this optimised approach in creating high-quality cationic SAMs on Ag substrates, offering strong potential for sensor and surface-coating applications. • Developed a stable, uniform method to anchor triethylammonium-functionalised self-assembled monolayers on silver surfaces Ag. • Identified ethanol as the optimal solvent, achieving a contact angle reduction to 5.85° for hydrophilic surfaces. • Produced defect-free monolayer coatings for sensors and surface applications. • Established a robust streamlined approach for applications in sensors and surface coatings.