Design of Nanostructured Protective Coatings with a Sensing Function

Corrosion-Responsive Self-Healing Coatings

Organic coatings are one of the most popular and powerful strategies for protecting metals against corrosion. They can be applied in different ways, such as by dipping, spraying, electrophoresis, casting, painting, or flow coating. They offer great flexibility of material designs and cost effectiveness. Moreover, self-healing has evolved as a new research topic for protective organic coatings in the last two decades. Responsive materials play a crucial role in this new research field. However, for targeting the development of high-performance self-healing coatings for corrosion protection, it is not sufficient just to focus on smart responsive materials and suitable active agents for self-healing. A better understanding of how coatings can react on different stimuli induced by corrosion, how these stimuli can spread in the coating, and how the released agents can reach the corroding defect is also of high importance. Such knowledge would allow the design of coatings that are optimized for specific applications. Herein, the requirements and possibilities from the corrosion and synthesis perspectives for designing materials for preparing self-healing coatings for corrosion protection are discussed.

Anticorrosion Coating with Heterogeneous Assembly of Nanofillers Modulated by a Magnetic Field

An anticorrosive coating with randomly distributed passive barriers and regionally enriched active corrosion inhibitors is developed by integrating mica nanosheets (MNSs) and magnetic-responsive core-shell mesoporous nanoparticles with 2-mercaptobenzothiazole (Fe₃O₄@mSiO₂/MBT) under magnetic field incubation. The bottom enriched Fe₃O₄@mSiO₂/MBT rapidly releases the MBT to form a passivation layer on corrosion sites, enhancing the corrosion inhibition efficiency by 30.36% compared with the control (NP_0.7EP-R). The impedance modulus |Z|_0.01 Hz of the sample (NP_0.7/MNS_0.5/EP) increases by five orders of magnitude compared with that of its control (NP_0.7/MNS₀EP) after 30 days of corrosion immersion. NP_0.7/MNS_0.5/EP exhibited the lowest corrosion rate (3.984 × 10^-5 mm/year) as compared to the other samples. Notably, the coating in a fractured state still maintains superior corrosion inhibition even after 40 day salt spray testing. The differentiated distribution of nanofillers was well confirmed by optical microscopy and SEM-EDS, and the synergistic effect of the active/passive integrated anticorrosive coating with merits of both comprehensive protection and fast responsiveness was systematically explored.

Optically Sensitive and Magnetically Identifiable Supraparticles as Indicators of Surface Abrasion

Identifying and ensuring the integrity of products plays an important role in today's globalized world. Miniaturized information taggants in the packaging surface are therefore required to monitor the product itself instead of applying external labels. Ideally, multiple types of information are stored in such additives. In this work, micrometer-sized core-shell particles (supraparticles) were developed to provide material surfaces with both an identifier and a surface abrasion indication functionality. The core of the supraparticles contains iron oxide nanoparticles that allow identification of the surface with a spectral magnetic code resolved by magnetic particle spectroscopy. The fluorescent silica nanoparticles in the supraparticle shell can be abraded by mechanical stress and resolved by fluorescence spectroscopy. This provides information about the mechanical integrity of the system. The application as surfaces, that contain several types of information in one supraparticle, was demonstrated here by incorporating such bifunctional supraparticles as additives in a surface coating.

Supraparticles with a Mechanically Triggerable Color-Change-Effect to Equip Coatings with the Ability to Report Damage

Small scratches and abrasion cause damage to packaging coatings. Albeit often invisible to the human eye, such small defects in the coating may ultimately have a strong negative impact on the whole system. For instance, gases may penetrate the coating and consequently the package barrier, thus leading to the degradation of sensitive goods. Herein, the indicators of mechanical damage in the form of particles are reported, which can readily be integrated into coatings. Shear stress-induced damage is indicated by the particles via a color change. The particles are designed as core-shell supraparticles. The supraparticle core is based on rhodamine B dye-doped silica nanoparticles, whereas the shell is made of alumina nanoparticles. The alumina surface is functionalized with a monolayer of a perylene dye. The resulting core-shell supraparticle system thus contains two colors, one in the core and one in the shell part of the architecture. Mechanical damage of this structure exposes the core from the shell, resulting in a color change. With particles integrated into a coating lacquer, mechanical damage of a coating can be monitored via a color change and even be related to the degree of oxygen penetration in a damaged coating.