Hybrid Silica (SiO2/PDMS) anticorrosive coating: EIS-analysis and effect on functional group in PDMS chain

Corrosion is a physico-chemical phenomenon that affects all metal surfaces, including aluminum. The application of anticorrosive coatings is a conventional method employed to prevent corrosion. In this paper, we present the synthesis and characterization of hybrid coatings based on silica modified using polydimethylsiloxane containing methyl and methylphenyl groups in its linear chain. The synthesis was conducted using a polycondensation catalyst (di-butyl dilaurate tin; DBTL) and in the absence of a solvent. Infrared spectroscopy indicates the formation of two silica clusters and the presence of the main functional groups. The bonding of silicon (D) in the linear siloxane chain at 1260 cm ^–1 with the silica clusters formed from TEOS is observed. The Si–O–Si bond was identified with an intense signal at 10 cm⁻¹ and a shoulder at 1200 cm⁻¹. In addition, TGA–DSC analysis corroborated the formation of a polysiloxane chain bonded to the formed silica. Furthermore, atomic force microscopy (AFM) revealed a modification in the microstructure of the coatings. Coatings comprising PDMS–CH ₃ demonstrated an increase in roughness with linear chain content (0.79–2.37 nm) and the formation of non-uniform needle-like particle structures. In contrast, coatings formed by the PDS chain show an average roughness of 3.69 nm (which contains a phenylmethyl group in the linear chain), with the formation of spherical particles bonded and deposited over the entire surface. The functional group has been demonstrated to modify the anticorrosive behavior of the ceramic. This conclusion is supported by the results obtained by EIS, which show that the Restimated, defined as the diameter of the semicircle in the Nyquist diagram, increased by 10-16 times for uncoated aluminum, 28-33 times for the SiO ₂ /DMS-CH ₃ coating, and 28-33 times for the SiO ₂ /PDS coating. These findings indicate that the SiO ₂ /PDS coating exhibits a greater anticorrosive capacity than the SiO ₂ /DMS-CH ₃ coating, particularly as the siloxane chain content in the ceramic increases. Furthermore, the PDS functional group (CH ₃ and phenyl) demonstrates a greater effect on the anticorrosive behavior.