A group of researchers has found a new method to create ultrathin surface coatings that are water resistant, self-healing and tough enough to survive scratches and dings. The new material was developed by combining thin films and self-healing technologies.
Through a study conducted by Nenad Miljkovic, mechanical science and engineering professor, and Christopher Evans, materials science and engineering professor, from the University of Illinois Urbana-Champaign, the researchers were able to create a new ultrathin surface coating.
According to this study, the rapid evaporative qualities of a specialized polymer containing a network of dynamic bonds in its backbone help form a water-resistant, self-healing coating of nanoscale thicknesses. Furthermore, the coating is robust enough to resist scratches and dings.
This new material, developed by merging self-healing technologies and thin-film, finds a wide spectrum of potential applications, including self-cleaning, anti-icing, anti-fogging, anti-bacterial, anti-fouling and enhanced heat exchange coatings.
The goal of the research
The research team's main goal was to increase the efficiency of steam power plants, which are the largest generators of electricity in the world, by using this type of coating in their condensers.
“The coatings, when applied to the surfaces of the condensers, make them more water-resistant and efficient at forming water droplets, which optimizes heat transfer,” said graduate research assistant Jingcheng Ma, a co-lead author of the study.
According to the researchers, thin coatings used in steam power plants can run into various durability problems. Coatings can break down in a week and sometimes even a in few hours. Such a short duration makes the real-world application of the coatings an ongoing challenge. This has been a fundamental problem in mechanical and materials sciences for about eight decades as although thicker coatings are more durable, they reduce heat transfer and erode the underlying benefits of the coating.
Previous studies have revealed that most ultrathin coatings have small pinhole defects after being cured on the surface. Steam penetrates through these defects, resulting in the gradual delamination of the coating. Therefore, the researchers' goal was to develop a pinhole-free, water-resistant thin film and improve the overall energy efficiency of steam power plants by several percent.
Called dyn-PDMS, the material can be easily dipped onto nanoscale layered materials on various surfaces such as silicon, aluminium, copper or steel.
“Self-healing materials can recycle and reprocess themselves. We have found that we can successfully utilize the healing enabled by dynamic bonds, allowing coatings to self-repair in response to scratching or to prevent pinhole growth”, Evans said.
“One of the reasons we can get such thin layers is because the solvents used in the reaction evaporate very quickly, leaving only the polymer,” the professor continued. “Also, once cured, the material repairs itself from scratches very quickly, so fast it's hard to see it in real time. We do not see this behaviour in large, bulk samples of the material, only in the thin film, and this is a question we are trying to answer now”.