Effect of Polyelectrolyte Order on the Efficiency of Smart Particles Constructed via Layer-by-Layer on a Silica Substrate

Organic coatings are widely used to protect metallic surfaces against corrosion. However, failures in these coatings can expose the metal to corrosive agents, reducing their effectiveness. To overcome this limitation, the incorporation of corrosion inhibitors into smart particles has been studied. These particles release the inhibitors in a controlled manner in response to external stimuli, such as pH variations. In this context, silicon oxide particles (P-SiO₂) are being investigated as promising reservoirs, with their effectiveness depending on the gradual release of the inhibitor.
This study addresses the incorporation of the corrosion inhibitor methylimidazole into mesoporous P-SiO₂ using the Layer-by-Layer (LbL) technique to develop a nanostructured film on the particle surfaces. Alternating layers of branched polyethyleneimine (PEI) and type B bovine gelatin were applied, along with the inhibitor itself. The particles were characterized by zeta potential (ZP) measurements and ultraviolet-visible (UV-Vis) spectroscopy, while corrosion tests were conducted to evaluate the effectiveness of the coated particles.
The methodology involved preparing PEI and gelatin solutions at 0.2% (w/v) concentrations, adjusted to pH 10, and incorporating methylimidazole at 0.01 mol.L⁻¹. Three types of P-SiO₂ were studied: calcined, non-calcined, and non-calcined washed, to assess their capacity for inhibitor incorporation and release. The LbL assembly was carried out through successive adsorption and centrifugation steps, followed by drying at 60 ºC for 24 hours. The final configuration of the smart particles varied depending on the type of P-SiO₂ used.
The results showed that PEI exhibited a positive ZP (+15 mV), while gelatin exhibited a negative ZP (-15 mV), confirming the electrostatic interaction between the polyelectrolytes. The release analysis of methylimidazole via UV-Vis indicated that non-calcined particles with the first PEI layer exhibited the highest inhibitor release rate, making them promising for anti-corrosion applications. This behavior suggests that selecting the appropriate layer configuration can optimize the efficiency of corrosion protection systems.
The anti-corrosion efficiency was calculated based on mass loss (ML) in environments with and without the corrosion inhibitor, according to ASTM G1:03 standards. The tests demonstrated that the addition of smart particles to the NaCl solution reduced ML by 20.61% compared to the specimen exposed only to NaCl, highlighting that these particles improve the protection of X65 steel against corrosion in saline environments.