Cleaning with spit, and now with pillars and pancakes

Last month human saliva got its due, with the awarding of the 2018 Ig Nobel Prize for chemistry, as an effective agent to clean surfaces. This month, pillars and pancakes are served up as an effective way to pattern surfaces so that those surfaces will be self-cleaning.

Pillar/pancake details are in the new study “Pillars or Pancakes? Self-cleaning surfaces without coating,” Naureen Akhtar, Peter J. Thomas, Benny Svardal, Stian Almenningen, Edwin de Jong, Stian Magnussen, Patrick R. Onck, Martin Anders Fernø, and Bodil Holst [pictured here]. Nano Letters, epub 2018.

The authors, at the University of Bergen, Norway and the University of Groningen, The Netherlands, report:

“Surfaces that stay clean when immersed in water are important for an enormous range of applications from ships and buildings to marine, medical and other equipment. Up till now the main strategy for designing self-cleaning surfaces has been to combine hydrophilic/hydrophobic coatings with high aspect ratio structuring (typically micron scale pillars) to trap a (semi-)static water/air layer for drag and adhesion reduction. However, such coating and structuring can [bring unwanted side-effects]. Here we present a radically different strategy for self-cleaning surface design: We show that a surface can be made self-cleaning by structuring with a pattern of very low aspect ratio pillars (“pancakes”). Now the water is not trapped. It can flow freely around the “pancakes” thus creating a dynamic water layer. We have applied the new pancake design to sapphire windows and made the first surfaces that are self-cleaning through structuring alone without the application of any coating. An offshore installation has now been running continuously with structured windows for more than one year. The previous uptime for unstructured windows was 7 days.”