Not only are fingerprints on shiny stainless-steel surfaces unattractive, but they also attack the surface. A new nanocoating that is being developed by Fraunhofer researchers will prevent the smudges that result from a finger touching stainless steel surfaces. The key to their approach is a special nanoparticle that is added to the coating.
The shiny new refrigerator features an attractive stainless-steel front. But it does not take long before the door is covered in fingerprints that are difficult to remove with only a cloth and detergent, the job actually calls for some arduous polishing. Fingerprints like these are more than just unattractive to look at, the grease film also attacks the metal surface.
Together with their colleagues at FEW Chemicals GmbH in Wolfen, the researchers from Fraunhofer Institute for Microstructure of Materials and Systems IMWS in Halle are now working to put an end to fingerprint smears like these. The secret is in a coating layer that contains special additives, and which is water and oil repellent.
The effects of these layers are twofold when the particles integrated into the coating settle on the surface of the stainless steel, the surface becomes rougher and it's surface area increases. When a finger comes into contact with the refrigerator door, it only touches the raised points on the surface and the grease on the fingertip never reaches the valleys of the stainless-steel surface.
The surface area which actually comes into contact with the grease is kept small. The refractive index of the coating has been adjusted so that it matches that of the natural oil content of the skin. This means that the light is reflected by the coated stainless-steel surface in about the same manner as by a surface that has been touched by sticky fingers. As a result of this, the fingerprints are not as noticeable.
While FEW Chemicals GmbH is handling the development of the coating systems, the Fraunhofer team is concentrating on the analysis of these layers.
"We're investigating the layers created using not only optical microscopy, but also scanning electron microscopy and atomic force microscopy. We look at how large the individual particles in the coating system are and whether or not they are distributed homogeneously. The effect of the additives used is another focus of our analysis," says Dr. Jessica Klehm, a research associate in the business unit Biological and Macromolecular Materials at Fraunhofer IMWS.
There are a lot of challenges had to be overcome before these investigations could be conducted. First, the samples had to be reduced in size. Optimum investigations with optical microscopy as well as a further investigation with other methods require the samples to have a thickness of no more than 60 to 80 micrometers which is about the thickness of a human hair, an examination that is under a transmission electron microscope even requires a sample that is one thousand times thinner.
"We can't cut the samples to size using a saw, which would destroy the coating. Therefore we embed the samples in resin and then grind them down to the desired thickness," Dr. Klehm explains.
The researchers have found a favorite among the various coating systems that they have investigated. The task now is to further optimize the system. Development activities should be completed by the end of 2020, which the industrial-scale production of the coating system will be turned over to a FEW Chemicals GmbH.
