# The charged drop sharpened before impact

After sliding about 4 cm over an insulator, a saltwater drop formed a cone near coated copper. After 3,000 charged impacts, local defects appeared. The neutral control remained smooth.

Study: H. Li and colleagues, “Electrification of water drops triggers corrosion of water-repellent surfaces”, *Nature*, 26 August 2026, [DOI 10.1038/s41586-026-10941-6](https://doi.org/10.1038/s41586-026-10941-6). Article and materials licensed CC BY 4.0.

## 1. The observation

The two supplementary recordings show different shapes before contact. The neutral drop keeps a smooth arc. The charged drop forms a cone. These are not trials that differ only in charge: the control falls directly, while the charged drop first slides over PFOTS-treated quartz.

A separate control keeps the sliding path and discharges drops through a tungsten wire. After roughly 1,000 impacts, charged drops damaged the coating boundary while grounded drops did not.

## 2. The charge path

The Figure 2 source workbook contains 20 measurements at each of three positions:

- +2.037 nC after sliding and before impact;
- +1.837 nC recorded at the copper connection;
- +0.0158 nC left in the drop after impact.

The calculation 0.0158 ÷ 2.037 shows that 0.78% of the incoming charge remained in the drop. By difference, 99.22% left it; 90.2% was measured at the copper connection. The simple balance does not locate the remainder.

## 3. After 3,000 impacts

The target placed 35 nm of copper beneath a 60 nm Teflon AF1600 coating. The neutral control used 35 µl, 1 mM NaCl drops at 12-second intervals. Its surface remained smooth. Drops charged after sliding over four insulators left local defects.

This result shows a morphological change. Chemical identification of corrosion products comes from a separate, harsher test using 50,000 drops and 10 mM NaCl.

## 4. The proposed mechanism

The authors propose this chain: sliding electrifies the drop; metal concentrates the field; the dielectric coating breaks down locally; repeated defects let water reach the copper. The final steps were not directly filmed at microscopic scale.

## 5. Conditions and boundary

- Drop: 35 µl, 1 mM NaCl.
- Slide: about 4 cm over a surface at 50°.
- Final fall: about 5 mm.
- Target: 60 nm Teflon AF1600 over 35 nm copper, tilted 10°.
- Charge produced by the four surfaces: about 0.2 to 2 nC.

The study shows a possible laboratory mechanism. It does not measure defect frequency, mean affected area, effects in natural rain, or the contribution to corrosion on buildings, vehicles, or ships.

## 6. Sources

- [Nature article](https://www.nature.com/articles/s41586-026-10941-6)
- [Supplementary information](https://media.springernature.com/original/springer-static/esm/art%3A10.1038%2Fs41586-026-10941-6/MediaObjects/41586_2026_10941_MOESM1_ESM.pdf)
- [CC BY 4.0 licence](https://creativecommons.org/licenses/by/4.0/)

Last checked: 28 August 2026.