Giant mobility of surface-trapped ionic charges revealed by sliding water droplets

Publication / Research

On September 10, 2025

Electrostatic mapping of surface charges
Electrostatic mapping (short times on the left, long times on the right) of surface charges deposited in the wake of a water droplet sliding on a hydrophobic solid. Their lateral diffusion over time highlights a remarkably high mobility.
A team of researchers from ESPCI Paris (CNRS/PSL/Sorbonne Université) and the Laboratoire Interdisciplinaire de Physique (CNRS/Université Grenoble Alpes) combined high-resolution electrostatic mapping with molecular dynamics simulations to investigate the behavior of these surface-trapped ionic charges. They found that the ionic charges spread across the surface with astonishing mobility. Their two-dimensional diffusion far exceeds that of ions in bulk water, with the limiting factor being the friction between the ionic solvation shell and the solid.

These findings, published in Proceedings of the National Academy of Sciences, reveal the existence of a new state of interfacial ionic matter, which the authors term “ionic puddles.”

Date

On September 10, 2025

Contact

Simon Gravelle
simon.gravelleatuniv-grenoble-alpes.fr (simon[dot]gravelle[at]univ-grenoble-alpes[dot]fr)

Submitted on September 2, 2025

Updated on September 10, 2025