Researchers from RMIT University and the University of Melbourne have discovered that water generates an electrical charge up to 10 times greater than previously understood when it moves across a surface.
The team, led by Dr Joe Berry, Dr Peter Sherrell and Professor Amanda Ellis, observed when a water droplet became stuck on a tiny bump or rough spot, the force built up until it “jumped or slipped” past an obstacle, creating an irreversible charge that had not been reported before.
The new understanding of this “stick-slip” motion of water over a surface paves the way for surface design with controlled electrification, with potential applications ranging from improving safety in fuel-holding systems to boosting energy storage and charging rates.
“Most people would observe that rainwater drips down a window or a car windscreen in a haphazard way, but would be unaware that it generates a tiny bit of electrical charge,” said Sherrell, whose research at RMIT’s School of Science specialises in capturing and using ambient energy from the environment.
“Previously, scientists have understood this phenomenon as occurring when the liquid leaves a surface, which goes from wet to dry.
“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.
“Importantly, this charge does not disappear. Our research did not pinpoint exactly where this charge resides, but clearly shows that it is generated at the interface and is probably retained in the droplet as it moves over the surface.”
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.
“Understanding how and why electric charge is generated during the flow of liquids over surfaces is important as we start to adopt the new renewable flammable fuels required for a transition to net zero,” said Berry, who is a fluid dynamics expert from the Department of Chemical Engineering at the University of Melbourne.