By Nick Gilbert
For several years, scientists have been devising methods to learn the hydrophobic nature of the lotus leaf. Directed by Aalto University, an international research team has resolved a new concept of scripting and displaying information on surfaces with water. The unique property of a trapped layer of air, and its effect on a lotus-based dual-structured water-repelling surface immersed in water, supported the research.
A superhydrophobic surface causes the water-repellency nature of the lotus leaf. The presence of microscopic surface structures eliminates the entry of water. As a result, a thin layer of air is formed between water and the surface. While being immersed in water, the entire surface is covered by a trapped air layer.
Directed by Dr. Robin Ras at Aalto University in Finland, the researchers of Nokia Research Center, and University of Cambridge created a surface having structures in two size scales such as tiny nanofilaments and microposts measuring equivalent to 10 µm. This two-level surface can have air layers that exist in two wetting states similar to two size scales. Switching between the two states can be achieved locally using a nozzle that generates over- or underpressure within the water for fluctuation of the air layer to either state.
However, there is an alteration only in the shape of the air layer while switching; the solid surface remains unchanged. Based on contrast between the states, shapes are scripted down on the surface underwater and the sample is then removed from water. This demonstration shows a dry surface without having any trace of the writing.
Tuukka Verho of Aalto University developed the method for manipulating the air layer using a nozzle. He demonstrated that reversible switching can be precisely performed in a pixel-by-pixel fashion.
Being published in PNAS, an article titled “Reversible switching between superhydrophobic states on a hierarchically structured surface” gives detailed description on this project.