Layer-By-Layer Deposition of Graphene Oxide-Based Coatings for the Protection Of Archaeological Metallic Objects

The protection of archaeological bronze from environmental corrosion requires solutions that overcome the limitations of traditional polymeric treatments. This thesis develops and validates an innovative protective coating based on graphene oxide (GO) assembled via the Layer-by-Layer (LbL) technique with poly(diallyldimethylammonium chloride) (PDDA), offering a water-based, potentially reversible application protocol aligned with modern conservation principles. Three GO fractions with defined lateral sizes, Small GO (SGO, ~5 µm), Large GO (LGO, ~23 µm), and Ultra-Large GO (ULGO, ~32 µm), were isolated by centrifugation. The LbL deposition protocol was optimised on model substrates (silicon wafers and quartz slides), where all fractions exhibited linear film growth with bilayer number and single-bilayer surface coverage ranging from 88% (SGO) to 97% (ULGO). Coatings were then applied to copper oxide surfaces simulating archaeological patinas and their protective efficacy evaluated by potentiodynamic polarisation (Tafel analysis) and electrochemical impedance spectroscopy (EIS) in 0.1 M NaCl, and by accelerated ageing under HCl vapour. Surface changes were quantified by colorimetry, SEM-EDS, XRF, and micro-Raman spectroscopy, and compared to the standard Paraloid B-72 treatment. All GO/PDDA configurations surpassed Paraloid B-72 in Tafel inhibition efficiency (>89% vs 86%), with SGO 2-bilayer reaching 98.2%. EIS analysis indicated that the nanometric coating thickness and aggressive electrolyte conditions limited the resolution of the coating barrier contribution, suggesting the need for milder test environments in future characterisation. In accelerated ageing, ULGO 2-bilayer achieved the highest Protection Factor (≈82%), with post-ageing analysis confirming substrate preservation without crystalline corrosion products. All coatings remained below the perceptibility threshold on archaeological-type surfaces (ΔE* < 5), compared to ΔE* ≈ 14 for Paraloid B-72. These results demonstrate that GO/PDDA coatings via LbL assembly offer tuneable barrier properties, superior aesthetic neutrality, and flexibility to tailor coating architecture to specific conservation scenarios, representing a promising alternative for the protection of archaeological bronze.