Smart Nanostructured Coatings Containing Graphene Oxide and pHResponsive Polyelectrolytes for Corrosion Protection of 2024 Aluminum Alloy

A smart nanostructured multilayered coating based on sol-gel/ polyelectrolytes/inhibitor/graphene oxide is developed via layer-by-layer (LbL) technique to provide effective corrosion protection for Al2024 substrates. The multilayered coating is consisting of a strong polycation (i.e., poly diallyldimethylammonium chloride (PDADMAC)), a weak polyanion (i.e., poly acrylic acid (PAA)), a corrosion inhibitor (i.e., Benzotriazole), and graphene oxide (GO). The local pH change in case of corrosion cause the loss of electrostatic attraction between polyelectrolytes, leading to increased permeability of the polyelectrolyte layer. Consequently, the corrosion inhibitor is released to prevent the corrosion process, providing a self-healing effect. Besides, the graphene oxide acts as a barrier layer, preventing the permeation of water and corrosive agents. The morphology, structure and chemical compositions are characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDS). To ensure the deposition of graphene oxide layer, Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy are performed. UV-visible spectrophotometry (UV-vis) is used to study the pH responsive release of corrosion inhibitor. To study the corrosion resistance and self-healing properties, electrochemical impedance spectroscopy (EIS) is performed in 3 % NaCl. The samples with polyelectrolyte layer show improved corrosion protection compared to the sol-gel sample (control). However, the samples with graphene oxide show the highest resistance, which is ~10X higher than the control sample after 2 weeks and its value is equal to 105.42 ohm.cm2.