Scientists have discovered that water generates much more charge as it moves across surfaces than previously thought, especially when it sticks to tiny obstacles and slides past them. This new discovery could revolutionize surface design, allowing for safer fuel storage, better energy storage, and faster charging technology.
Researchers from RMIT University and the University of Melbourne have discovered that the charge generated by water as it moves across the surface is 10 times stronger than previously thought.
The research team, led by Dr Joe Berry, Dr Peter Sherrell and Professor Amanda Ellis, found that when a water droplet encounters tiny bumps or rough spots on the surface, it builds up strength until it suddenly "jumps" or "slides" past the obstacle. This movement creates a long-lasting charge that scientists have never observed before.
This new understanding of the "stick-slip" motion of water opens the door to designing surfaces that can be controlled electrified. Potential applications include improving the safety of fuel storage, enhancing energy storage and increasing charging efficiency.
Sherrill, whose research at RMIT University's School of Science focuses on capturing and harnessing electrical energy from the environment, said: "Most people will observe rain dripping randomly from a window or car windscreen, but they are not aware that rainwater generates a weak electric charge. Previously, scientists thought this phenomenon occurred when the liquid leaves the surface, that is, when it changes from wet to dry. In this work, "We have shown that when the liquid first touches the surface, that is, from dry to wet, a charge is generated that is 10 times stronger than the wet to dry charge. Importantly, our study does not pinpoint exactly where this charge occurs, but clearly shows that it is generated at the interface and may remain in the droplet as it moves across the surface."
"As we begin to adopt the new renewable flammable fuels required for the transition to net zero, it is important to understand how and why liquids generate charges as they flow over surfaces," said Berry, an expert in fluid dynamics at the University of Melbourne's Department of Chemical Engineering. "Shocking inside a fuel container containing flammable liquids is extremely dangerous, so installation of a charger after the liquid has moved is required. This knowledge can help us design coatings that can reduce charge in new fuels. "Currently, for existing fuels, charge accumulation can be reduced by limiting flow, using additives, or other measures." "
In the study, published in Physical Review Letters, the team studied this charging effect using water and materials used in polytetrafluoroethylene (PTFE).
Teflon is a plastic commonly used in pipes and other fluid-handling materials, but it does not conduct electricity, which means the charge generated cannot be safely or easily removed.
The team measured the charge and contact area created as water droplets spread and contract on a Teflon flat plate, effectively simulating the movement of a water droplet on the surface, and then used a specialized camera to capture individual frames of the droplet adhering and sliding while measuring changes in charge.
"We were lucky enough to have three excellent chemical engineering master's students help set up and run our experiments as part of the University of Melbourne course," Berry said.
First author Shuaijia Chen, a PhD student at the University of Melbourne, said the charge generated when water first contacts the surface changes the most, from 0 to 4.1 nanocoulombs (nC).
As the water interacts with the surface, alternating between wet and dry phases, the charge swings between about 3.2 and 4.1 nanoamperes.
"To put this into perspective, the amount of charge generated by water moving across the surface of Teflon is more than a million times smaller than the electrostatic shock you might get by jumping next to someone on a trampoline. This amount of charge may sound trivial, but this discovery could lead to innovations that enhance or dampen the charge generated by liquid-surface interactions in a range of practical applications," Chen said.
The team says the impact of this research depends on co-developing commercial technologies with future industry partners.
The researchers plan to study stick-slip phenomena in other types of liquids and surfaces.
"The amount of charge and rate of charge in other liquid and surface material interactions could be relevant to a range of potential commercial applications," Sherrell said. "We plan to study how stick-slip motion affects the safe design of fluid handling systems, such as those used to store and transport ammonia and hydrogen, as well as methods for recovering electrical energy from the movement of liquids in energy storage devices and accelerating charging."
Compiled from /ScitechDaily