CHEMISTRY 2000

Topics of Interest #1:Nanotechnology and

Flexible Computer Screens

Janus Balls and Flexible Electronic Displays

Silica (a lattice with empirical formula SiO2) forms a variety of common materials including sand, glass and quartz.

Recent research has shown that silica can also be used to make microscopic spheres of different colours when it is injected into a particular resin. The colours come from light reflected by the fcc lattice and can be “fixed” by using UV light to cure, or set, the resin. Carbon black can be used to give the spheres a black side as well as a coloured side when they are first formed:

S-H Kim, S-J Jeon, W.C. Jeong, H.S. Park and S-M Yang Advanced Materials (2008) 20, 4129-4134; summarized in Nature (2008) 456, 4.

Janus Balls and Flexible Electronic Displays

The Janus balls are about 200 m in diameter. The images below show (a) a section of the flexible resin, and (b) what the resin looks like through an optical microscope. The idea is that, eventually, each Janus ball could be a pixel on a display screen.

S-H Kim, S-J Jeon, W.C. Jeong, H.S. Park and S-M Yang Advanced Materials (2008) 20, 4129-4134; summarized in Nature (2008) 456, 4.

Janus Balls and Flexible Electronic Displays

These tiny spheres are not only coloured on one side and black on the other, they also have dipoles that cause them to rotate in response to an electrical field. In order to give them the freedom to do so, the resin can be swelled by adding a solvent before the electrical field is applied.

One advantage of this technology is that the colour seen is not dependent on the angle at which the viewer is looking at the resin:

S-H Kim, S-J Jeon, W.C. Jeong, H.S. Park and S-M Yang Advanced Materials (2008) 20, 4129-4134; summarized in Nature (2008) 456, 4.

Janus Balls and Flexible Electronic Displays

While all the images so far have shown black/green spheres, Janus balls can be made in a variety of colours (red and yellow shown below).

Work is ongoing to make the “black side up” view blacker before this method can be used for marketable displays.

S-H Kim, S-J Jeon, W.C. Jeong, H.S. Park and S-M Yang Advanced Materials (2008) 20, 4129-4134; summarized in Nature (2008) 456, 4.