As we develop extremely liquid repellent surfaces, the errors in existing measurement techniques are getting too large — ScienceDaily
How liquids are repelled by the surface – a property called "wetting" – important for engineers developing aircraft that resist icing; developing outdoor equipment that rejects rain and dirt for fashion designers; Researchers who develop new surface materials in the laboratory in various fields between the two also need to accurately measure the wetting properties in order to compare the performance of different surfaces. For more than two centuries, standard methods of how droplets and surfaces interact have been defined by measuring the "contact angle" of the droplets. The contact angle is the angle between the edge of the drop and the surface on which it is placed. Aalto University's research is now being questioned in a perspective article published in the journal Science on March 15th.
The Problem with the Contact Angle Method – According to Professor Robin Ras – it depends on the accuracy of the camera used to image the droplets and the subjective decision surface that the scientist encountered at which position of the droplet in the image. As scientists and engineers develop more and more waterproof materials, our ability to measure their effectiveness is reduced, as measurement errors are greatly reduced as drainage capacity increases.
Professor Ras's team carefully quantified the errors in contact angle measurements, and his team is investigating alternative methods of measuring how water-repellent surfaces interact with droplets. Newer methods of measuring adhesion or friction between surfaces and droplets not only have lower errors, but also allow for physical quantification, which is more relevant to engineers developing new materials.
"We encourage researchers to rethink the correlation of contact angles in hydrophobic surface features and propose force as the next generation benchmark," Professor Ras said.
By improving the understanding of the scientific community, where there is a better way to measure surface wettability, Professor Ras and his team hope that others can use traditional measurement techniques to further discover findings that are currently unavailable.
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