Researchers from RMIT University and the University of Melbourne have discovered that water moving across a surface generates an electrical charge up to 10 times greater than previously understood.
The findings, published in Physical Review Letters, could have implications for energy storage, fluid handling systems, and safety in fuel storage.
The research team, led by Dr Joe Berry, Dr Peter Sherrell, and Professor Amanda Ellis, observed that when water droplets became stuck on tiny bumps or rough spots, they built up force before “jumping or slipping” past the obstacle.
This motion, known as “stick-slip,” resulted in an irreversible charge that had not been previously reported.
Sherrell, from RMIT’s School of Science, explained that while rainwater dripping down a window may seem random, it actually generates small amounts of electrical charge.
“Previously, scientists have understood this phenomenon as occurring when the liquid leaves a surface, which goes from wet to dry,” he said.
“In this work we have shown that charge can be created when the liquid first contacts the surface, when it goes from dry to wet, and is 10 times stronger than wet-to-dry charging.”
Berry said an electric shock inside a fuel container with flammable liquids could be dangerous, so charge build-up on a solid surface needs to be safely discharged after a liquid has moved on.
The study focused on water interacting with polytetrafluoroethylene (PTFE), commonly known as Teflon, a material frequently used in fluid handling systems.
Since PTFE does not conduct electricity, any generated charge remains trapped on the surface. Using high-speed cameras, the researchers measured charge variations as water droplets spread and contracted over a flat PTFE plate, simulating real-world conditions.
PhD student Shuaijia Chen, the study’s first author, noted that the first contact between water and the surface produced the largest charge change, from 0 to 4.1 nanocoulombs (nC).
Researchers said the charge oscillated between about 3.2 and 4.1 nC as the water-surface interaction alternated between wet and dry phases.
Looking ahead, the researchers plan to explore the stick-slip phenomenon with different liquids and surfaces.
Sherrell indicated that their future work will focus on applications in fluid handling and energy storage.
“We plan to study where stick-slip motion can affect safety design of fluid handling systems, such as those used to store and transport ammonia and hydrogen, as well as methods to recover electricity and speed up charging from liquid motion in energy storage devices,” Sherrell noted.
The research team is seeking industry partners to explore commercial applications of their findings.
