Nov 06, 2023 14:00:00

``Super water-repellent material'' is developed that allows water droplets to slide down the surface with almost no friction

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Water repellency ', a phenomenon in which attached water droplets roll on a surface like a ball, is used to improve the waterproof performance of car bodies and rain gear such as umbrellas. A research team led by Sakari Repikko of Aalto University in Finland has developed a material that allows water droplets to slide off the surface with almost no friction, making it harder for water droplets to adhere than conventional water-repellent materials.

Droplet slipperiness despite surface heterogeneity at molecular scale | Nature Chemistry
https://www.nature.com/articles/s41557-023-01346-3

Researchers create the most water-repellent s | EurekAlert!

https://www.eurekalert.org/news-releases/1005284

Repicco and his team used specially designed equipment to create a thin layer of silicon, called a self-assembled monolayer (SAM), just one molecule thick.

They were covalently bonded to form a film on the surface. Specifically, the SAM layer is created by spraying a chemical called octyltrichlorosilane onto silicon material using a vapor deposition device. The SAM layer formed on the surface of the silicon material acts as a lubricant between the silicon surface and water droplets, and has the property of repelling water droplets.

Lepicco claims, ``Our research is the first to create a molecularly heterogeneous surface at the nanometer level.''

The research team also used a polarimeter to closely observe the formation of the film. In addition, the coating rate of the formed film was varied by adjusting conditions such as the temperature of the vapor deposition equipment, moisture content, and deposition time. As a result, it was found that by shortening the adhesion time and lowering the SAM coverage rate, the hydrophilicity, which allows water droplets to blend into the material and flow more easily, increases. On the other hand, it has become clear that when a substance is left on the surface for a long time, the water droplets become granular and tend to roll off.

'Our experimental results show that the sliding of water droplets on the surface is enhanced both when SAM coverage is low and high,' said Repicco. 'We thought that this would not make much of a difference in the slipperiness of water droplets.The results of this experiment contradicted that intuition.'

Regarding this discovery, Repicco said, ``This technology can be used not only for heat transfer in pipes, ice removal, and anti-fogging, but also for microfluidics, which requires the smooth movement of small droplets, and for removing adhered dirt. It could also be useful in creating self-cleaning surfaces that can be easily removed.'The main problem with current SAM coatings is that they are very thin and can easily be removed by physical contact.' In the future, we plan to conduct basic research toward practical application while improving durability.'