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Different approaches have been considered for the development of smart anticorrosive coatings by the incorporation of nanocontainers loaded with corrosion inhibitors into the protective layer. Nanocontainers are designed to allow a controlled release of the inhibitor in response to an external stimulus, thus, achieving more efficient and more economical use of the active component. In this case, a pH change is a very interesting stimulus to trigger the release because corrosion processes cause local pH changes. To this end, a special focus has been placed on the use of mesoporous silica nanoparticles (MSN) as nanocontainers due to their interesting characteristics, such as larger surface area, versatile functionalisation, stability, etc. However, the use of hollow mesoporous silica nanoparticles (HMSN), with a large central hole combined with an external mesoporous silica shell, offers an additional advantage due to the higher loading capacity. In the present work, HMSN have been efficiently synthesised, loaded with sodium phosphomolybdate, as a non-toxic alternative to the use of chromates, and encapsulated by a layer of an oppositely charged polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA). The morphology and textural properties of the produced nanocapsules have been studied by different techniques (SEM/EDS, TEM/EDS, Brunauer–Emmett–Teller (BET) analysis method, ζ-potential). Finally, the releasing capacity and corrosion protection at different pH values have been studied, confirming the smart behaviour of the encapsulated loaded HMSN.

Nowadays there is a special interest to study and develop new smart anticorrosive pigments in order to increase the protection life time of organic coatings and, simultaneously, to find alternatives to conventional toxic and carcinogenic hexavalent chromium compounds. In this respect, the great development of nanotechnologies in recent years has opened up a range of possibilities in the field of anticorrosive paints through the integration of encapsulated nanoscale containers loaded with active components into coatings. By means of a suitable design of the capsule, the release of the encapsulated corrosion inhibitor can be triggered by different external or internal factors (pH change, mechanical damage, etc.) thus preventing spontaneous leakage of the active component and achieving more efficient and economical use of the inhibitor, which is only released upon demand in the affected area. In the present work, the improved anticorrosive behaviour achieved by encapsulated mesoporous silica nanocontainers filled with an environmentally friendly corrosion inhibitor has been evaluated. It has been proven that a change in the pH allows the rupture of the capsules, the release of the inhibitor, and the successful protection of the carbon steel substrate.

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