We don’t think about high-performance surfaces, but we encounter them in everyday life. The decorative properties of surface coatings get noticed, but we don’t often think about what other performance properties they might have. Most surfaces achieve their performance qualities from the coatings applied to them. High-performance coatings could be divided into passive and active coatings. Active coatings are often called “Smart Coatings.” These coatings change their performance in response to external stimuli such as sunlight or damage to the coating film. Whether passive or active, these coatings enhance any substrate they are applied to, making them high-performance surfaces.
Often several high-performance attributes are combined in one coating system. This may be achieved by applying several layers like a primer and a topcoat or formulating with multiple functional components. Recently, researchers have developed self-stratifying coatings which spontaneously form discrete layers after application. For example, after application, anticorrosive components would migrate to the coating/substrate interface while components preventing biofouling migrate to the outer surface.
Corrosion resistance is one of those properties we only notice by its absence. Preventing substrate corrosion is one of the most important functions of a coating since corrosion inflicts billions of dollars worth of damage annually. This is one of the earliest “high-performance coatings,” developed even before the phrase was in common use. As soon as objects were made from iron and steel, corrosion became a problem, and attempts were made to prevent it with coatings. Certain pigments were found to interfere with the electrochemical processes of corrosion, and high-performance coatings were born.
As anticorrosive coatings matured, drivers outside of performance shaped their development. Some of the most effective corrosion preventers were extremely toxic and banned from use. Many of the nontoxic replacements do not perform as well as the old standbys. Innovative materials and formulation techniques are being used to improve the performance of nontoxic corrosion inhibitors. Reactive corrosion preventing ingredients can be micro-encapsulated and released as the coating wears or is damaged. This controlled release enables long-term corrosion resistance while improving the performance of the safer nontoxic corrosion inhibitors.
Surfaces exposed to marine environments, whether on ships or fixed structures such as wind turbine installations, require high-performing coatings which prevent corrosion and biofouling. Similar toxicity concerns have eliminated many of the antifouling agents historically used in marine coatings. Micro-encapsulation can also be utilized to improve the performance of nontoxic compounds, which prevent build-up of marine organisms on vessels and structures. The combination of micro-encapsulated anticorrosive and antifouling agents could be used in separate coating layers or in a self-stratifying coating to distribute the respective components where they are most effective.
Maintenance is required to sustain a high level of performance over the lifetime of a coated surface. Repairing and touching up damaged areas of the coating and cleaning dirt or other contaminations from the surface are periodically needed. High-performance coatings can also incorporate self-maintaining properties that sustain performance without external intervention. The high-performance surface coatings of the future will be able to maintain themselves as well as provide unique properties such as antimicrobial activity. The key to properly maintaining a surface is preventing damage in the first place.
Abrasion is a common damage mode for surfaces, and formulating coatings to resist abrasion increases performance and longevity. The self-stratifying coating concept can be used to increase abrasion resistance by distributing selected materials into the air/coating interface region. These materials, for example, nano-silica particles, selectively harden the surface to resist damage from abrasion. Once damage occurs, whether from abrasion, cracking or erosion of the surface, self-repairing coatings can work to restore the coatings performance. Micro-encapsulation of reinforcing polymers that rupture when coating damage occurs can repair damaged films.
Contamination also prevents the optimum performance of a surface. Coatings can be formulated to remove contamination without maintenance. Besides making a surface visually unappealing, dirt contamination can impair other properties such as reflectance and sanitation. Various materials and formulation techniques can impart cleaning and sanitizing abilities to a surface coating. Distributing these components to the air/coating interface through self-stratification increases their effectiveness. Techniques such as high surface tension or the Lotus effect, using microstructure to repel contamination, provide self-cleaning surfaces with low maintenance requirements. The pandemic has increased interest in antimicrobial coatings, which facilitate sanitary surfaces in hospitals, schools and public spaces.
High-performance surfaces do require high-performing surface coating. These are not single-purpose products either. Combinations of formulation materials and techniques such as micro-encapsulation or self-stratification impart a variety of high-performance properties in one coating.
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