Two
unrelated scientific teams are researching
waterproof surfaces. The two teams looked to two different
naturally occuring waterproof substances for their model, but they both do the same thing. A team in
Japan, headed by
Zhong-Ze Gu took the
Morphu sulkowskyi butterfly with its water-repellent wings as a model for its research. These butterflies have incredibly beautiful colored wings, and coincidentally, the coating created in the
Japanese laboratory also comes with
iridescent colors.
The substance is made by assembling silica particles (6 nanometers wide) and polystyrene spheres (several hundred micrometers wide) into a film. Then this substance is heated to remove the polystyrene. The areas of the film formerly occupied by the polystyrene is replaced with air gaps. This leaves a rough surface of just silica particles. The process is not completed, however. To this film is added a layer of fluoroalkyailane, a waterproof compound that has been commercially available for some time.
An interesting fact to note is that by manipulating the size of the air gaps in the film, the color of the the substance changes. Scientists have created versions of the compound in colors ranging from red to blue to an almost colorless compound.
This color manipulation is not only cosmetically interesting, but also environmentally sound. It would allow for waterproof covering for commercial products without dyes to make them aesthetically pleasing, such as cameras or watches. The colorless version of the compound could be used as a covering for windows.
The other teams used the lotus flower, with its water and dirt repellant coating, as its model. A. Levant Demirel, working at Koç University and a team of researching scientists at Kocaeli University in Istanbul have reported that they have created what they call a “superhydrophobic” coating to be used from a common plastic. This plastic is very easily produced and costs very little. This plastic is called isotactic polypropylene, or iPP.
This simple coating is made by dissolving iPP in organic solvents, placing the solution on glass slides and evaporating the solvents. What is left over is a plastic film that “resembles a bird’s nest.” This film resembles the coating of the lotus leaf very closely.
Both the Japanese and Turkish versions of the plastic film resist water and dirt very efficiently. Both water and dirt bead up on the surface and roll off instantly.
Source: Science News
Vol. 163, No.9 – March 1, 2003
Title: “Waterproof Coats: Materials repel water with simplicity, style”