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Wednesday, 18 September 2019
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Raw materials & technologies, Technologies, Functional coatings

Researchers develop fabrication method for superhydrophobic surfaces

Friday, 31 August 2012

New technology can be used to manufacture large-scale water repellent surfaces on silica. Scientists hope it can lead to innovative self-cleaning materials.

Singapore-based scientists have developed a new fabrication method for superhydrophobic surfaces

Source: Nanadou/ Fotolia

Singapore-based scientists have developed a new fabrication method for superhydrophobic surfaces

Source: Nanadou/ Fotolia

Linda Yongling Wu at the A*STAR Singapore Institute of Manufacturing Technology and co-workers have developed a fast and cost-efficient way to fabricate large-scale superhydrophopic surfaces on a hard material - silica. The researchers used a laser to carve out a microstructured template that they then used to pattern a sol-gel coating. Nanoparticles were subsequently bound to the surface of the cured sol-gel surface to create a second level of hierarchy. The fabrication methodology can be adjusted to achieve different degrees of micro- and nanostructures.

In addition to the new fabrication methodology, Wu and co-workers considered various ways to optimise the water repellency of the textured surface. They found that increasing the surface roughness increases the true area of contact between the liquid and the solid, enhancing its intrinsic wetting properties. However, if the surface features are small enough, water can bridge protrusions leading to the formation of air pockets; the wettability of such a nanostructured material is then calculated as a weighted average of the wettability of the pure material and that of air. These two effects are known respectively as the Wenzel and Cassie-Baxter states.

Optimum superhydrophobic effect

The researchers derived an equation for calculating the surface contact angle between a water droplet and a silica surface with a certain degree of roughness. They found that there was a transition between the Wenzel to the Cassie-Baxter state, as surface structuring enters the nano dimension. The researchers found that for an optimum superhydrophobic effect, the Cassie-Baxter state must dominate the surface structure to allow a massive 83 % of the surface state to be involved in air trapping with only 17% of the liquid drop surface actually in contact with the silica itself.

The researchers are hoping that their findings will generate new ideas for making innovative self-cleaning materials. "We are now developing the technology for real applications, such as easy-clean coating for solar films and structured surfaces for personal care products,” says Wu.  

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