Image Courtesy: Katharina Maisenbacher / MPI-P
Raindrops may seem harmless, but new research suggests they can gradually damage protective coatings through tiny electrical discharges. Scientists found that water droplets can pick up an electrical charge as they move across surfaces, then release that energy when they strike a coating, creating microscopic damage.
The discovery could help explain another way outdoor paints and protective coatings deteriorate over time, potentially affecting everything from garden fences and cars to major landmarks such as the Eiffel Tower and Golden Gate Bridge. The study was led by researchers from the Max Planck Institute for Polymer Research, the University of Bonn, South China University of Technology, MIT, and Johannes Gutenberg University Mainz.
Paint and other coatings are typically thought to deteriorate through mechanical and chemical processes. Repeated impacts from water can gradually erode surfaces, while acids, salts, and other substances in water can trigger chemical damage.
The new research points to electricity as another contributor. Water droplets can become charged as they slide across a surface, a phenomenon known as frictional electrification. When those charged droplets later hit a protective coating, the accumulated charge can discharge in a tiny flash.
Researchers tested the effect using Teflon, a material known for its resistance to water and chemicals. When uncharged droplets were repeatedly dropped onto the coating, the researchers found no visible changes even after 3,000 impacts.
The results changed when the droplets were first allowed to roll across other materials, including a plant leaf, PVC, and polystyrene. The contact caused the droplets to accumulate electrical charges before they struck the Teflon.
After another 3,000 impacts, microscopic examination revealed changes not only in the Teflon coating but also in the metal beneath it.
The amount of charge generated varied substantially depending on the surface. Zhongyuan Ni, the study’s first author, said the researchers measured differences of up to a factor of ten between materials. Despite those variations, detectable changes occurred in every experiment involving charged droplets.
The researchers say the findings reveal an overlooked pathway through which water can weaken protective coatings. Understanding the electrical effects could eventually help engineers design surfaces that better withstand weather exposure.
The research, published in Nature, could have applications ranging from protecting historic landmarks and vehicles to improving the durability of everyday outdoor coatings.
