Charged raindrops can pierce protective coatings, new research shows

Researchers led by Zhongyuan Ni, Rüdiger Berger and Hans-Jürgen Butt at the Max Planck Institute for Polymer Research in Mainz, Germany, have identified a previously overlooked mechanism behind rain-driven corrosion. Their study focused on "slide electrification," where water droplets acquire electric charge as they glide over insulating surfaces such as leaves, painted walls, or plastic panels. In controlled tests, 35-microliter drops containing a pinch of salt slid down tilted substrates before falling onto a copper plate coated with a 60-nanometer Teflon film.

The charged drops, measured at up to two nanocoulombs (several thousand volts), punched tiny holes through the coating, mimicking a miniature spark. This electrical penetration differs from the traditional view that rain merely abrades or chemically attacks protective layers. The results imply that electric discharge may play a significant role in the degradation of corrosion-resistant coatings in real-world conditions.