Human skin has an amazing capacity to heal itself from scratches and cuts, so it’s not surprising that scientists are looking at transferring the self-healing properties of skin to materials. Efforts to embed tiny liquid-filled capsules that rupture when a scratch occurs to spill healing agents into the damaged area of electroplated coatings have previously been hampered by the size of these capsules. But now researchers have developed a process for producing electroplated layers with nano-capsules that measure only a few hundred nanometers in diameter that could solve the problem.
Previous capsules, which measured 10 to 15 micrometers, were too large for the electroplated layer, which is itself around 20 micrometers thick. The researchers from the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart, together with colleagues from Duisburg-Essen University, found that, although shrinking the capsules down to the nanoscale solved this problem, it presented another challenge.
The difficulty then became ensuring that the smaller capsules and their thinner and more sensitive casings weren’t damaged when producing the electroplated layer – a process that involves electrolytes that are extremely aggressive chemically and can easily destroy the capsules. The solution lay in finding a compatible material for the capsule casing depending on the electrolytes used – the details of which the researchers are choosing to keep under their hats.
Self-healing materials are of particular interest to the car-makers because of the potential for self-healing paint to combat the various scrapes and scratches vehicles are prone to. But self-healing materials have applications well beyond the automotive industry. One example is for mechanical bearings, which usually have an electroplated coating in which the capsules can be embedded. If there is a temporary shortage of lubricant and part of the bearing’s coating is lost, the capsules at the top of the layer will burst and release lubricant to prevent any damage to the bearing.
The researchers have produced the first copper, nickel and zinc coatings with the new capsules, although surface coverage does not extend beyond the centimeter scale. They estimate that it will be another one and a half to two years before whole components can be coated.
The team is also working on more complex systems involving differently filled capsules whose fluids react with one another like a two component adhesive.