Functional coatings: "an extremely exciting field for protecting the environment"

Modern features make coatings more sustainable, add value and make everyday life easier. We interviewed Gesa Patzelt of Fraunhofer IFAM to find out how functional coatings work, how to develop them, and how to prepare for the short and long term markets.
Dr. Gesa Patzelt, Ph.D., Frasahofer IFAM,
Dr. Gesa Patzelt is the project leader of Fraunhofer IFAM in Germany

. She will hold a functional coatings workshop in October.
is the definition of a functional coating?
. Gesa Patzelt: When asked about different experts, the definitions are slightly different. Ultimately, the general properties of the coating, such as corrosion protection or decoration, should be supplemented by other functions. These properties are broad in scope and can be defined differently for a variety of applications.
, for example, in the aerospace industry, these include anti-pollution, anti-ice, erosion stability, but also reduce the flow resistance on the wings. Ultimately, all fuel-saving technologies. In principle, many developments are triggered by environmental protection, such as the topic, because one wants to reduce carbon dioxide2 emissions. That's why functional coatings are also a very exciting area that helps protect the environment.
's not just about the airline industry?
: Yes, there are anti-fouling coatings in this area to prevent microbes from growing on board. Currently, biocides are mainly used for this purpose, but some of them have been banned due to their toxicity. We are also developing functional concepts as an alternative. Here, we can help reduce marine pollution. On the one hand, by using fewer fuels such as heavy oil, on the other hand, by using little or no biobicides.
are there specific examples of functional coatings already on the market?
Patzelt: Yes, this is the self-healing wood varnish we developed with Adler-Werk Lackfabrik. The coating contains microcapsules. If damage is caused by hail, a self-healing agent formed by the capsule appears from the capsule and protects the wood substrate as the cracks formed are partially filled.
also some coatings are about to be commercialized. For example, we developed a paint with a microstructure that mimics shark skin. This is used for aviation and wind energy thresholds and is designed to reduce wall friction resistance.
a classic functional coating, how about an easy-to-clean coating?
Patzelt: Here are some things that have been used for a long time. For example, everyone knows lotus. In principle, the durability of an easy-to-clean coating is not ideal. This is a general problem with functional coatings.
's why?
Patzelt: Each case is different. To understand this, you must know how to create features. The easiest way is to use additives to achieve functionality. They can be moved in a polymer substation and migrated to the surface to function there. However, they can also disappear from the coating in this way. Of course, the additive's storage will eventually run out.
you must also understand how functional additives fit into the formulation and whether all other additives and fillers and pigments used in the formulation are compatible with these additives. Incompatibilities that result in lower resistance can also occur. As a result, polymer substrings that are consistent with this are generally better developed and may interlink with active substances. In this case, the stability is much higher.
but it sounds more complicated.
Patzelt: Yes, it's a little complicated. However, other errations can also be coupled with additives, which then interact with the polymer substring. For example, isocyanate can interact and interlink with the OH group of an additive. In this way, the substances are firmly combined and do not migrate to the surface, where they can be anchored directly and can be used for longer periods of time.
now have two strategies, one is to add additives in the traditional way and the other is to add additives in a fixed way. Are there any other strategies?
: Of course, I mentioned microcapsules earlier. Here, the chemical structure of the material to be ensconced is decisive. Different substances can be encapsulated, depending on whether they are in a watery or solvent-containing environment. This would also be an example of a storage that exists in the coating but is released only by damaging it again in this case.
's not just about self-healing. For example, fluorescent dyes are also ensconced and then act as an indicator when the coating is damaged. This is useful for materials that have a certain tendency to crack and are not necessarily clearly visible.
addition, we have a concept in which we show the top layers of evenly distributed fillers and then functionalize them for later use. Or you've functionalized particles exposed to plasma. The prerequisite is that the plasma does not change its erration. These microcapsules ensure that the protective function of the self-healing coating is maintained.
are there any concepts that can optically restore the initial state?
Patzelt: Yes, but they're further away from the app. This is the field of internal self-healing, where self-healing originates from polymers. There is a metallic polymer in the polymer substitum, which is first separated but then redirected at the time of damage, or by hydrogen bonds, and then redirected after damage and completely repaired again.
a ph.D. thesis from Fraunhofer IFAM, which showed that the self-healing of the polymers studied here applies only to certain humidity. This means that there is always some kind of trigger that can repair itself, which means that the coating cannot be used worldwide.
so far, we've focused on the various features. Can you also create two or three different features?
Patzelt: There must be features that can be combined with each other. For example, elastomer coatings with very good erosion stability can also be made hydrophobic, making them easy to clean or anti-fouling.
but features sometimes have a negative impact on each other. For example, the structure of the coating can be affected. Of course, it would be great to have a coating for all functions, but unfortunately that won't work.
if we look to the future, will it be important in functional coatings?
Patzelt: In general, the topic of structured surfaces is interesting when it comes to different phobias, namely the combination of hydrophobic and oil-sparing surfaces. This is a way to reject dirt or insects, which are made up of many different components.
still have a lot of direction. In particular, we need to understand the interactions between microscopic and nanostructures, their combinations, and the ideal appearance of the structure.
, for example, we cannot predict in advance how certain structures will affect ice testing or anti-pollution testing. If we fully understand this, we will be able to move more in the direction of the toolbox in the future.