By giving it a liquid-like coating that defies usual designs, water will roll off the surface at angles 500 times shallower than other superhydrophobic materials.

The ability to repel water is important for many materials, particularly in the automotive, marine and aerospace industries. Many superhydrophobic surfaces work by trapping a layer of air or liquid, which causes any water that lands on it to ball up into droplets and roll off more easily. But an emerging technology creates what are called liquid-like surfaces (LLS), which have layers of highly mobile molecules that act like liquids but are tethered to substrates so they don't escape. The end result is like a lubricated surface that water slides right off.

In the new study, scientists at Aalto University in Finland developed a new LLS out of molecules called self-assembled monolayers (SAMs) coating a silicon substrate. By tuning conditions like the temperature and water content in the reactor during production, the team could control how much of the silicon the SAMs covered.

When the SAMs covered much of the surface, it became superhydrophobic, causing water to form droplets and roll off. That in itself was to be expected – but to the surprise of the researchers, low SAM coverage also made for a slippery surface. And it did so without the water beading, which has long been thought to be necessary for superhydrophobicity.

"It was counterintuitive that even low coverage yielded exceptional slipperiness,' said Sakari Lepikko, lead author of the study. "We found that, instead, water flows freely between the molecules of the SAM at low SAM coverage, sliding off the surface. And when the SAM coverage is high, the water stays on top of the SAM and slides off just as easily. It's only in between these two states that water adheres to the SAMs and sticks to the surface."