Il Woong Park is doing his research in the laboratory, imitating nature’s own surfaces. (Photo by Maren Agdestein / NTNU)
In the world, there are two types of surfaces. One is the friend of water, while the other is not. They are called the hydrophilic surface and the hydrophobic surface. Why do your clothes repel water droplets when it rains? How can we avoid ice getting attached to a glass window or on the road? Why can some surfaces repel water but not oil? How can a surface remove more heat, for example, helping to cool down your mobile?
These questions are all connected to the characteristics of the surfaces that we are facing every day. Thus, gaining control of the characteristics of the surface can open to unexpected new developments – maybe in the future allowing ice-free windows or smaller mobiles.
Nature has also had similar issues – like the relationship with water. Plant leaves have been evolving to overcome the problem, and therefore developing extraordinary behaviors. For example, a Lotus leaf stays dirt-free even when the plant lives in muddy places, without using detergent or energy the leaf can remain clean. This is possible because of its extreme water repellency (superhydrophobic).
Another interesting example, is the Ruellia Devosiana leaf achieving an impressive rapid spreading of water (superhydroph ilic). The fast-spreading creates a larger water-air interface for more evaporation. It is important to survive in rainforests which have high densities of precipitation. In order to check what is different between the two, I have observed them under the microscope. From those structures in small scale, I got the inspiration to copy the surfaces from nature.
Nanotechnology brings us new tools for mimicking nature’s structures in a small scale. Moreover, it opens the possibility to develop new surfaces with new properties. During the past year, I was looking into how to replicate these structures on the silicon surfaces. After many attempts, I was able to replicate the conical micro structures.
To do this, two technics were adopted: One is photo-lithography, which is the printing technique like an old photography technique. The other is the plasma etching, which is a cutting technique using the small accelerated ions. With the prepared samples, I checked how close they are to water. Finally, one of the reasons why they act differently is observed in this work. The details of the study are available in this publication Advanced Materials Interfaces.
Il Woong Park
This blog post was written by PhD candidate Il Woong Park, at Department of Energy and Process Engineering, NTNU. He belongs to the thermal two-phase flow laboratory.
His group is also working in NTNU Nanolab