Scientists Discovered a Mysterious Force Eating Away at Cars, Bridges, and Monuments

3 min readHere’s what you’ll learn when you read this story:In recent years, scientists have explored how water can gain a positive electric charge while sliding along insulating surfaces, a phenomenon known as slide electrification. In a new study, researchers show that these miniscule-yet-frequent charges break down coatings, causing surface damage. Understanding this flaw could help companies develop better coatings to protect important cultural sites and infrastructure.Leave a metal alone in the rain long enough—even with protective coatings—and eventually, corrosion will do its work. While auto manufacturers do their best to shield their four-wheeled chariots from the elements, water still finds a way to work its slow damage. Scientists originally hypothesized that the physical impact of water on a surface might be why it’s so strongly corrosive (and if you’ve been in a big enough storm, you can probably attest to this fact), and they also proposed that acidic compounds might play a role.However, a new study published in the journal Nature suggests that a third source of corrosion might be at work, one that acts similarly to when two solids rub against each other—a process known as “tribocharging.” In the study, a team of researchers led by scientists at the Max Planck Institute for Polymer Research in Mainz, Germany, studied water that traveled across insulating surfaces—such as leaves, window glass, PVC foam boards, and quartz—before striking a surface coated in a non-conductive substance (aka Teflon). They recorded that these water droplets accumulated anywhere from 0.2 nanocoulombs of a charge (on a leaf) to around 2 nanocoulombs (on quartz). Those are small charges, but they’re enough to do some serious damage over time. This process is known as “slide electrification,” a phenomenon initially explored by some of the same authors in a previous study in 2025.At first, there appeared to be no perceived difference in damage after hundreds of impacts, but then a casual idea by the study’s lead author, Zhongyuan Ni, prompted a breakthrough.“One day, I just let the experiment [keep] running,” Ni told Science News. “I forget; I [went] to drink coffee or something.”What Ni found upon his return were undeniable signs of damage, which prompted the team to investigate further. They ran two versions of the same experiment—one where droplets slid down a material before hitting a Teflon-coated surface, and one where the droplets didn’t slide. After 3,000 hits, they found that the former experiment produced signs of damage to the coating where the other did not—even when viewed under a microscope.“This is a kind of ‘friction electricity’ in droplets and is physically much more complex than previously assumed,” Max Planck Institute’s Rüdiger Berger, a co-author of the study, said in a press statement. “When such charged droplets strike a coating, they discharge locally and can puncture the layer in specific spots like a small flash of lightning—with consequences for the coating’s durability.”So what happens when sliding water strikes a coated surface? First, water accumulates a positive charge through slide electrification. The metal underneath the coating responds with a negative charge of its own, and the attraction between them sets up an electric field. Then as the droplet falls, scientists use high-speed cameras to document a front-forming cone similar to a Taylor cone (as seen when electrostatic force acting on a liquid overcomes surface tension and creates a deformation). Essentially, as the droplet approaches the surface, it creates an electric field that increases as the two objects get closer, causing a dielectric breakdown on impact that produces chemical changes in the coating itself.“Corrosion is initiated by localized dielectric breakdown of the coating induced by charged drops,” the authors write. “As a result, the underlying metal becomes exposed to the aqueous drop environment. As more charged drops hit the surface, the defective area gradually grows.”The authors note that charged droplets don’t have to specifically rub against these materials to form—they can also be present in clouds, thunderstorms, ocean waves, and waterfalls. And if charged droplets are quietly drilling through protective layers, then the fix isn’t a tougher coating. What we need are coatings that give the charge somewhere to go. Engineers who account for that could buy years of extra life for bridges, pipelines, car bodies, and the monuments we’ve been struggling to preserve for centuries.Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.