Measuring how wet a surface can get

24 Mar 2020

A*STAR researchers have developed a modified version of atomic force microscopy to characterize liquid-repellent surfaces for various applications.

Look closely at any seafaring vessel and you might notice algae, plants and small animals like mussels attached to its hull. These hitchhikers cause a problem known as biofouling, compromising a ship’s performance (due to the additional weight that lowers the ship’s fuel efficiency) and affecting the vessel’s structural integrity.

Because the root cause of biofouling is long-term contact with water, tuning the wettability of the ship’s hull is key. However, characterizing the wetting properties of a material or surface is technically challenging, said Dan Daniel, a Research Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE).

“The conventional approach of studying wetting properties involves placing a droplet on the surface and looking at the angle it makes with the surface. While this is easy to do, it is also crude and does not yield much information about surface wettability,” he explained.

To obtain a more thorough understanding of surface wettability, Daniel and his colleagues used a modified form of atomic force microscopy (AFM). Conventional AFM involves the use of a solid silicon-based AFM tip to ‘sweep over’ a surface and quantify the atomic-level interactions between the tip and the surface. In this study, the researchers used a 40-wt% glycerin–water droplet of diameter 20 to 50 µm in place of the solid tip to glean insights into how a surface interacts with liquid at the atomic scale.

Applying their technique, Daniel’s team was able to measure the adhesion force and energy required to detach a water droplet from a surface, reporting that they were able to record forces with nanonewton precision. The researchers were also able to capture the rapid detachment of water droplets with millisecond resolution.

“Our technique can be used to objectively assess the effectiveness of various surface coatings and optimize their future design,” Daniel suggested. “I plan to also use this technique to quantify the forces required to extract crude oil from rocks under different conditions. The findings from such a study will have important implications for oil extraction and recovery,” he said.

The A*STAR-affiliated researcher contributing to this research is from the Institute of Materials Research and Engineering (IMRE).

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Daniel, D., Lay C. L., Sng, A., Jun Lee, C. J., Jin Neo, D. C. et al. Mapping micrometer-scale wetting properties of superhydrophobic surfaces. Proceedings of the National Academy of Sciences of the United States of Americ 116: 25008-25012 (2019) | article

About the Researcher

Dan Daniel obtained his PhD degree in applied physics from Harvard University, before joining A*STAR’s Institute of Materials Research and Engineering (IMRE) in 2017. He is currently a Group Leader of the Droplet Lab. His research interests are in droplet and aerosol physics.

This article was made for A*STAR Research by Wildtype Media Group