It is not exactly polite dinner table conversation, but there is an issue that materials science has finally addressed - the non-stick lavatory bowl. The research is not simply about hygiene and domestic aesthetics but could reduce the tens of billions of liters of water used to flush lavatories every day by reducing the amount needed per flush. Tak-Sing Wong of Pennsylvania State University and colleagues suggest that their coating could reduce flush volume requirements for treated toilets by approximately 90 percent. [Wong et al., Nature Sustain. (2019); DOI: 10.1038/s41893-019-0421-0]

The team has developed a two-stage spray-on material to create a liquid-entrenched smooth surface (LESS) coating that can easily be applied to ceramic toilet bowls. The first spray contains molecularly grafted polymer and builds an extremely smooth, liquid-repellent foundation. On to this foundation, a layer of lubricant is applied which fills the gaps between the polymer chains of the foundation layer.

Wang says that when they coated a toilet bowl in this manner and dumped simulated fecal matter into the bowl the material simply slides down the wall of the bowl. The viscoelastic synthetic feces do not stick to the surface and slip away leaving no residue. In a real toilet, this would preclude the need for either a second flush or use of the toilet brush and disinfectant bleach, for instance.

The team says that their coating essentially makes the toilet bowl self-cleaning but requires far less water to get rid of the waste. Their estimates suggest the coating would be functional for 500 flushes before the lubricating layer needs to be reapplied. The coating can repel solids with viscoelasticity spanning nine orders of magnitude; this is broader activity by three orders of magnitude compared with earlier coatings. Critically, the layer not only sloughs off slurry but it precludes the formation of bacterial films on the toilet bowl, again reducing the need for disinfectants of bleach and reducing some bathroom odors that might otherwise accumulate. They add that in places where waterless toilets are commonplace, the coating could improve sanitation considerably, particularly in those parts of the developing world where water is very scarce.

The work was carried out in conjunction with Leon Williams from the Centre for Competitive Creative Design at Cranfield University in the United Kingdom.

"With an estimated 1 billion or more toilets and urinals worldwide, incorporating LESS coating into sanitation systems will have significant implications for global sanitation and large-scale wastewater reduction for sustainable water management," the team concludes.