Hurrah! Urinals will soon be splash-free

Engineers have developed a new technique that could pave the way for splash-free urinals in the future.

When drops of liquid hit a hard surface at a high-speed, the impact distorts the liquid’s structure and it bounces back. The rebound motion of liquid can sometimes be unpleasant or even dangerous, and can certainly result in higher cleaning fees.

But, splashes could be a thing of the past as a paper published in Physical Review Letters [paywalled] reveals a surprisingly easy method that could prevent unwanted splashes - coat the surface with something soft.

Professor Alfonso Castrejón-Pita, lead-author of the research and engineer at the University of Oxford, said he was motivated to study splash dynamics as “no one had actually studied systematically what happens when droplets hit soft substrates.”

So, Castrejón-Pita and his team set about painstakingly analysing the 100,000 shots taken by recording splashing alcohol droplets with a high-speed camera. The frames were then combined with theoretical calculations and computer simulations to discover that tiny deformations of the drops happen within the first 30 microseconds after impact, and can be suppressed by using a soft surface.

“What is most surprising is that you need about 70 per cent more energy to get a drop to splash off these soft materials when compared with hard materials. If you think of a drop falling from a certain height, we need double the height to make it splash in the softest surfaces,” Castrejón-Pita said.

After splashing, drops can turn into aerosols or sprays spreading nasty liquids. A drop of ethanol or methanol will splash if dropped from a height of around 20cm, which can then be carried away by air, Castréjon-Pita said.

There other applications besides from splash-free urinals. It could prevent stop molecules that could bring of food-poisoning or harmful chemicals from spreading. The challenge is far from over though, as It’s not as simple as making a material soft, Castréjon-Pita said.

When a material is softer, it’s often stickier and weaker and doesn’t last as long-term coatings. The next task for the researchers is to try and find the right materials with the optimum stiffness that can last such as hydrogels.

It seems like fluid dynamics is a worthy area of research, as just last month physicists cracked the equations that describe the motion of spilling. If they keep this up the dry-cleaning industry could face a recession. ®