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The aim of this study was to develop smart materials with stimuli-responsive properties for the long-term protection of steel. The idea was to obtain a tailored and controlled release of protective agents in response to the environment stimuli. First, the protective efficacy of three inhibitors containing a carboxylic moiety, such as p-aminobenzoic (pAB), succinic (SA), and caffeic (CA) acids, was investigated in alkaline chloride solutions. The results revealed that pAB is the most effective protective agent, significantly better than SA and CA. It is surprising that the steel surface in the pAB solution remains unchanged even after 5 months of corrosion treatment, whereas the formation of degradation products in the SA and CA solutions was observed after only 6 days. Based on these findings, pAB was selected and used for the functionalization of silica nanoparticles and layered double hydroxides (LDHs) that can act as delivery vehicles and as an inhibitor reservoir. Specifically, pAB was chemisorbed on silica amino groups via an amide bond, and this makes possible a gradual inhibitor release induced by an alkaline environment. The intercalation of pAB in its anionic form into the LDHs structure is responsible for a completely different behavior since the release is induced by chloride ions and occurs by an anionic exchange reaction. Thus, these materials play a dual role by acting as an inhibitor reservoir and by capturing chlorides. These findings reveal that it is possible to create a reservoir of corrosion inhibitors gradually released on demand based on the chemical environment. The stimuli-responsive properties and the complementary protective action of inhibitor-loaded silica and LDHs make them attractive for the long-term protection of steel and open the way for innovative solutions in the preservation of concrete cultural heritage.

The photodegradation kinetics of 2‐mercaptobenzothiazole (MBT), a corrosion inhibitor for copper‐based alloys, is studied in high amorphous polyvinyl alcohol coatings subjected to either UV irradiation or indoor light exposure. The photodegradation process proceeds rapidly, thus compromising the anticorrosion ability of the coating. The encapsulation of MBT into layered double hydroxide (LDH) nanocarriers slows down its decomposition kinetics by a factor of three. Besides preserving the corrosion inhibitor, such a strategy allows a controlled release of MBT triggered by corrosion‐related stimuli, for example, presence of chloride species and acid pH. The developed coating guarantees long‐lasting corrosion protection even at low amounts of inhibitor‐loaded LDH nanocarriers (ca. 5 wt %). This also reflects in a high transparency, which makes the protective coating suitable for demanding applications, such as the conservation of high‐value metal works of art.

Two-component solvent-born polyurethane coatings for the protection of bronze from corrosion were prepared. Trisilanol-heptaisooctyl polyhedral oligomeric silsesquixane (POSS) nanoparticles were exploited to increase the coating protective efficiency. Its improvement was confirmed through a combination of characterisation techniques. In particular, the POSS addition caused an increase of the water contact angle, and an enhancement of the elastic connotation and abrasion resistance of the polyurethane coating. Potentiodynamic polarisation measurements also indicated that the coating containing POSS nanoparticles has an improved protection efficiency. Impedance spectroscopy revealed that the magnitude of low-frequency impedance of polyurethane coatings decreased more for the coating without POSS during exposure in electrolyte for thirty days. Ex situ IR reflection-absorption spectroelectrochemistry was exploited to get insight into the degradation of coatings during chronocoulometric charging at anodic potentials. IR reflection-absorption technique was also used to evaluate any possible effect of different stripper solutions on the bronze substrate.

The attractive physicochemical properties of chitosan make its derived materials promising candidates for the reliable and sustainable corrosion protection of metallic substrates. In this work, chitosan-based coatings embedding different corrosion inhibitors, i.e. benzotriazole (BTA) and mercaptobenzothiazole (MBT), were investigated for the protection of copper-based alloys, with the aim to extend their application to the preservation of works of art exposed to indoor atmosphere. The composition of the formulations was optimized paying particular attention to their potential application in the field of cultural heritage. To assess the efficacy of the coatings, tailored accelerated corrosion tests were carried out on bare and coated bronze substrates. Coated and uncoated alloy disks were characterized before and after corrosion treatments by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. Moreover, an image analysis protocol was defined to evaluate the extent of surface modifications after degradation treatments. The obtained results revealed that the chitosan-based coatings containing BTA and MBT fulfil the aesthetic criteria required in the field of cultural heritage and are able to inhibit the corrosion of bronze alloys. It is worth noting that a synergic effect between the chemical protection provided by the inhibitors and the physical one provided by the polymer matrix was observed. Our findings demonstrate that the developed systems are suitable for a reliable and more sustainable protection of indoor bronze artefacts, thus representing a promising alternative to commercial products and particularly taking advantage from the use of non-harmful solvents for their application and removal.

Protective coatings based on polymers synthesized from renewable sources (chitosan or an amorphous vinyl alcohol based polymer) have been prepared for the protection of bronze artifacts from corrosion. Besides acting as an effective barrier against corrosive species present in the environment, the efficiency of the coatings has been improved by adding corrosion inhibitor compounds (benzotriazole or mercaptobenzothiazole) to the formulations. The liquid medium of the formulations has been carefully selected looking at maximizing the wettability on the bronze substrate and optimizing the solvent evaporation rate. The minimum amount of inhibitor compounds has been optimized by performing accelerated corrosion tests on coated bronze substrates. The inhibitors have been directly dissolved in the coating-forming solutions and/or introduced by means of nanocarriers, which allow to control the release kinetics. The free dissolved inhibitor molecules immediately provide a sufficient protection against corrosion. On the other hand, the inhibitor molecules contained in the nanocarriers serve as long-term reservoir, which can be activated by external corrosion-related stimuli in case of particularly severe conditions. Particular attention has been paid to other features which affect the coating performances. Specifically, the adhesion of the protective polymer layer to the bronze substrate has been assessed, as well as its permeability properties and transparency, the latter being a fundamental feature of protective coating for cultural heritages. Finally, the protective efficiency of the produced smart coatings has been assessed through accelerated corrosion tests.