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When a drop of water falls on a glass top, there’s a splash.
As the bead strikes the glass, its momentum, until then moving downward, is transferred in a horizontal direction. This sudden redistribution of energy causes a sheet of the liquid, called a lamella, to peel off from the drop. It’s lifted up from the surface by a thin layer of gas between the sheet and the glass and by a difference in pressure acting on the sheet’s top and bottom sides. This lift causes the lamella to break up into droplets, creating a splash.
Scientists study this splash in detail because, in the words of a 2014 paper in Physical Review Letters, it’s present in several “technological and scientific fields [including] ink-jet printing, combustion, and surface coating.”
A disorderly splash can create unwanted effects in these processes. For example, ink deposited on a sheet of paper by a printer could create a smudge. Sometimes splashing is also beneficial. In a coal power plant, the feedwater entering the boiler could accumulate dissolved carbon dioxide, which needs to be removed or it could corrode the boiler vessel. To do this, cold feedwater is first splashed on a surface. The splash produces droplets that are collected in a vessel, through which steam from a turbine is passed. As the feedwater heats up, it releases its dissolved carbon dioxide, which is blown through a vent. Then the feedwater enters the boiler.
Splashing is an important physical phenomenon and understanding it is key to improving many industrial processes. That way, they may even be able to eliminate splashing altogether. A new study from researchers from China, Germany, Hong Kong, and Switzerland has reported just this.
According to the group, splashing can be prevented altogether if a water drop falling on a hard surface is electrically charged. The findings were published in Physical Review Letterson April 1.
The team’s experiment was simple. A syringe needle releases water drops to a glass surface half to two feet below. On the way, the droplet passes through a copper hoop. The hoop and the needle are connected in an electrical circuit. When the drop passes through the hoop, it becomes electrically charged.
Video recordings revealed that when the charged drop hit the surface a lamella was formed — but it didn’t lift. The charges on the lamella pulled it towards the surface and kept it from spreading out. In the end, the splash was much smaller. The researchers found that beyond a particular charge, created by tuning the electric field inside the hoop, the drop made no splash at all.
They also found the effect only happens when the drop falls on an insulating surface. An electrically conducting surface would take away the charge, leaving the drop to make a splash. “Our results … highlight the potential of controlling splashing by manipulating drop charges,” the researchers wrote in their paper.
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Published – April 07, 2025 02:49 pm IST
