Water is one of the Earth’s most abundant resources, 97% of it is saline that covers three-quarters of the Earth’s surface, and only 3% is freshwater, which is essential for daily human life. While expecting 2.5% is blocked in the polar ice caps, glaciers, and atmosphere, only 0.5% of water can be used for humans in the form of river water and groundwater. Now 30% of the world’s population lacks access to clean water sources for fundamental sanitation needs.

Rain as part of freshwater can be collected. For relative drought areas like China Guizhou, the Middle East, southern Britain, Ethiopia, and India, they always have light rain and hard to collect.

In a study published in Langmuir, a research group from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) introduced a combination of femtosecond laser ablation and imprinting to fabricate superhydrophobic surface for high-efficiency rain collection.

They firstly used femtosecond laser to fabricate micro/nano gully structures on aluminum alloy surface. Imprinted micro/nano structures can come to the polypropylene (PP) surface.

The PP surfaces after imprinting had anisotropic property and excellent superhydrophobicity with the contact angles (CAs) greater than 160° and the sliding angles (SAs) smaller than 5° in parallel directions and smaller than 10° in the vertical directions. And the superhydrophobic PP surface had self-cleaning property.

The rain collection device made by using the superhydrophobic can reach an approximated maximum of 90%, more than 100% efficiency improvement of the device formed by flat PP surfaces in some cases for the light rain.

The rain collection efficiency and total surface area results showed that a rain collection device should have the sidewall at 10° angle for compact size and cost-saving and 30° angle for high rain collection efficiency, depending on the usage purposes. These data will help manufacture rain collection devices mainly applied to arid and drier countries and regions.