VUB revolutionises research into surface bonding
With his doctoral research on the effect of paint layers on metal, Dr Sven Pletincx, supervised by Prof Tom Hauffman and Prof Herman Terryn of the VUB research group Electrochemical and Surface Engineering (SURF), has succeeded for the first time in investigating the effects of salts or water on the contact layer between paint and metal under real conditions. “The new method will make it possible to examine all types of coatings in the future and even to tune the strength of the adhesion of the paint layers in advance. The research has implications for many areas ranging from the coating industry itself to applications in the construction and transport sectors,” says Dr Pletincx.
Paint layers flake off over time and lose their main function: to protect the underlying material. With metal, a paint layer protects against corrosion. The better the connection between the paint and the metal, the better the metal is protected. The bonds that form between the paint layer and the metal surface have been investigated for some time, but there were two major problems. The first problem is that a cross-section has to be made in order to examine the contact layer or interface, as a result of which it can already begin to react with the air. A second problem is that most conventional analytical techniques are done under vacuum conditions, at very low pressure.
“Current research methods do not simulate the real conditions to which paint layers are exposed,” explains Dr Pletincx. “In fact, research in the paint industry is currently carried out empirically, through trial and error. New coatings are made, adhesion is tested, the strength of bindings at the interface is tested. If the results are satisfactory, a new type of paint is available. This, of course, takes years and costs a lot of money.”
During his PhD, Dr Pletincx developed a method that makes it possible to examine the real paint layer under real conditions. The method is based on making the paint or metal layer very thin. Infrared and X-ray radiation are then used to examine the interface through the layers. At the same time, an electroanalytical technique developed at VUB is used, which provides additional information about the adhesion and the resistive and capacitive behaviour of the paint layer. Pletincx used this innovative method to study the effect of water and salts on the interface of the paint layers and the metal surface. The result was surprising from the start. It is generally assumed that water has a negative effect on bindings. However, the research revealed that for a certain type of acrylate coatings, water initially forms the bonds at the interface. As soon as more water is applied to the interface, the bindings break down as expected. The amount of water at the interface therefore plays an important role.
The new method makes it possible to examine the chemical characteristics of virtually all coatings in relation to time, temperature, amount of water, etc. Moreover, it will be possible to engineer the interfaces of coatings on metal surfaces and adjust the strength of the adhesion of the paint layers to the desired surface. The paint industry is looking for a flawless coating. The methodology of this PhD may be a step in the right direction.