Layer-by-Layer Assembly of PEI/Gelatin Films for Corrosion Inhibitor Incorporation

The layer-by-layer (LbL) deposition technique enables the fabrication of nanofilms by alternately depositing oppositely charged polyelectrolytes onto substrates. This method allows the construction of ultrathin films capable of incorporating molecules. Understanding polymer charge and zeta potential (ZP) is crucial for developing well-defined multilayer films and active coatings. Our goal is to create films with embedded anticorrosive molecules, using polymeric coatings to help mitigate corrosion damage in the future. In this study, films assembled using the LbL technique, incorporating the corrosion inhibitor imidazole (IM), were fabricated using the polyelectrolytes polyethyleneimine (PEI) and bovine gelatin type B on glass substrates. The PZ of PEI and gelatin was measured to determine their charge behavior at different pH values. Polymer mixtures were studied across a range of pH values to identify the conditions under which interaction occurred. The results showed significant interaction at pH 10, where PEI was positively charged and gelatin negatively charged. Based on this, LbL films were constructed at pH 10 to ensure optimal polyelectrolyte interaction for film formation. The resulting multilayer structure consisted of an ten-layer assembly in the following sequence: PEI/gelatin/PEI/inhibitor/PEI/inhibitor/PEI/inhibitor/PEI/gelatin, where imidazole was incorporated into three layers at concentrations of immersion solutions of IM (0.1 and 0.3 mol·L⁻¹ ), and PEI or gelatin at 0.2 (w/v%). The corrosion inhibitor release was tested by immersing the coated glass in HCl solutions at pH 4 and 2.5, with aliquots analyzed via UV-Vis spectroscopy. The studies revealed the zeta potential (ZP) values of PEI and gelatin at pH 4 and 10, showing opposite charges at pH 10. This confirmed pH 10 as the optimal condition for LbL film fabrication, where PEI exhibits PZ values around +15 mV, while gelatin shows negative values, close to -15 mV. Preliminary studies showed a difference in release as a function of inhibitor concentration for the releases monitored up to 30 minutes of the experiment. However, the release was similar for pH values of 4 and 2.5, remaining below 5 ppm up to 30 minutes of the experiment. The results confirm that pH 10 is ideal for the formation of LbL films, ensuring efficient interactions between PEI and gelatin. The inhibitor release varied with the initial concentration but was similar for pH 4 and 2.5. These findings contribute to the optimization of films for anticorrosion protection.