The toilet brush never has to leave its holder again. Researchers have created a super-content coating that helps start the road without leaving any traces.
The sprayed coating, which is smoother than Teflon, reduces the adhesion of even persistent stools by up to 90%, tests show, so much less water is needed to flush them away and leave the toilet clean.
Researchers at Penn State University believe that the coating can cut household water consumption and prevent odors and diseases from causing bacteria to build up in toilets.
"I was very happy to see how easily the stool slipped from our coated surface," Tak-Sing Wong at Penn State University told the Guardian.
Wong became interested in dirty toilets in 2015 when researchers at Cranfield University contacted him for help. They designed a toilet for use in the developing countries, but found that smelling waste was built up on the surface of the toilet bowl. "My research team was known for developing very slippery coatings to reject sticky substances," Wong explained.
He and his team spent the next few years developing a coating they call a "floating anchored smooth surface," or Less. It has two parts. The base layer binds to the toilet bowl and has protruding "nanohairs", each one billion times thinner than a human hair. To this, they add a fine coating of silicone oil, which is held in place by the base layer. All in all, the coating takes less than five minutes to apply.
After developing the coating, the researchers were eager to learn if it worked. And so began a series of eye-opening tests. First, they turned to a South African recipe for synthetic faeces and turned up a batch of different textures. To mimic fecal free fall, they dropped samples from a height of 40 cm to test plates angled at 45 degrees. Then, using a fluorescent dye mixed in the material, they measured how much water it took to release the false stools and remove all visible marks. The coated surface took 90% less water to clean than glass panels, the researchers found.
Then the researchers built a rig that dropped real human feces – from three anonymous donors – on a horizontal plate made of toilet ceramic, teflon, silicone or the researchers' coating. When falling feces had settled on the plate, the researchers released the platform so that it swung down like a window shutter and looked to see what was happening.
Wong, who founded a company to sell the coating, writes in the journal Nature Sustainability, describing how all comparison surfaces showed "extreme stickiness" in faeces, while the Less coating seemed to throw its load clean.
Further tests showed that the researchers' coating was better than conventional toilet surfaces to prevent bacteria from stools, urine or even rainwater from growing in the bowl. While the coating was stable enough to withstand 500 flushes, a test that simulated urination found that refilling after 50 "urination cycles" may be needed.
More than 141 billion liters of fresh water is used to flush toilets every day, or nearly six times daily water consumption in Africa, Wong said. With millions worldwide facing severe water shortages, he said he hoped that reducing the amount of water used for flushing could help alleviate the problem.
“People will know the effectiveness of non-stick frying in their lives, and a similar strategy for solving the stickiness problem is behind this ingenious material science. This time, the problem is not eggs sticking to a boiler, but poo sticking to the toilet pan, says Mark Miodownik, professor of materials and society at UCL.
“As this paper shows, such toilets would need less water per flush to clean them and also increase toilet hygiene. My only concern, which I'm sure the researchers will address as they continue their work, is what happens to the coating as it wears off through use – how would chemicals involved affect the environment if adopted globally?