Drops can become electrically charged as they slide across surfaces. If they then fall onto a coating—such as on a car—the coating can be corroded by the drop’s electrical discharge and permanently damaged. Credit: Katharina Maisenbacher / MPI-P

Charged raindrops may damage paint with tiny electrical discharges that act like microscopic lightning.

Weather gradually wears down painted and coated surfaces, something anyone who has had to repaint a fence has probably seen firsthand. The same problem affects far larger structures as well. Landmarks such as the Eiffel Tower and the Golden Gate Bridge require repeated repainting and maintenance to keep their protective coatings intact.

Scientists have traditionally blamed two major processes for this kind of deterioration. One is mechanical stress, where repeated impacts and friction from droplets slowly weaken a coating or cause pieces of it to flake away. The other is chemical damage, especially when water contains corrosive substances such as acids or salts.

A Hidden Electrical Source of Damage

Now, researchers have identified another factor that may contribute to coating failure: the electrical charge carried by water droplets.

The work was led by Hans-Jürgen Butt, director at the Max Planck Institute for Polymer Research, together with researchers from the University of Bonn, South China University of Technology, MIT, and Johannes Gutenberg University Mainz.

“A few years ago, we investigated the physics behind how water droplets become charged as they slide across surfaces. This is a kind of ‘friction electricity’ in droplets and is physically much more complex than previously assumed,” says Rüdiger Berger, group leader in the “Physics at Interfaces” department. “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.”

In other words, droplets can pick up electrical charge while moving across certain materials. When they later strike a coated surface, that charge can be released at a very small point, creating localized electrical damage.

Testing Thousands of Water Droplets

To test the effect, the researchers first released droplets onto a surface covered evenly with Teflon, a material widely known for its use on frying pans.

When the droplets carried no electrical charge, the coating showed no visible changes under a microscope, even after 3,000 impacts.

The team then changed the experiment by allowing droplets to roll across common materials before they hit the Teflon surface. These included a houseplant leaf, PVC, and polystyrene, such as that found in plastic windows.

As the droplets traveled across those surfaces, they accumulated electrical charge. They were then allowed to fall onto the Teflon coating.

After 3,000 charged droplets had struck the surface, microscopic examination revealed clear changes both in the coating and in the metal underneath it.

Different Surfaces Produce Different Charges

How much charge a droplet collected varied substantially depending on the material it crossed.

“The charge a droplet acquires as it slides depends heavily on the specific surface—we measured differences of up to a factor of ten,” explains Zhongyuan Ni, the study’s first author. “Regardless of this, we were able to detect changes in the coating in all experiments.”

The results suggest that electrical effects from moving water may be another important piece of the puzzle in understanding how protective surfaces deteriorate over time.

Toward Longer Lasting Protective Coatings

The researchers hope the findings, published in the journal Nature, could eventually help engineers develop coatings that are more resistant to this newly identified form of damage.

Such improvements could have applications ranging from cultural heritage sites and major infrastructure to cars and ordinary painted surfaces around the home, including the familiar garden fence.

Reference: “Spontaneously charged water drops induce corrosion” by Zhongyuan Ni, Xiaomei Li, Aaron D. Ratschow, Lin Jian, Xiaoteng Zhou, Pravash Bista, Diego Cortes, Gunnar Glasser, Haojian Luo, Shuai Chen, Jiyao Yu, Yongkang Wang, Katrin Amann-Winkel, Kaloian Koynov, Rüdiger Berger and Hans-Jürgen Butt, 26 August 2026, Nature.
DOI: 10.1038/s41586-026-10941-6

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