How To Erase Electronic Paper - New Product

The next big thing could be electronic paper – it can be written on, erased and used again - but the persistent problem is how to erase it. Electronic paper is composed of a checkerboard of cells that may be charged or uncharged.

University of Arizona chemist Jeanne Pemberton has been trying to work out how to erase the paper by studying the interface of ink and the tablet or paper at the nanolevel.

"Knowing how the surface charge affects the structure of ink molecules at the interface is key to figuring out how to repeatedly write on and then completely erase the paper", Pemberton said to the American Chemical Society.

By altering the electrical charges on the paper surface can control if ink sticks on the page or beads up. When a cell in the paper is uncharged, water molecules become more attracted to each other than the surface of the paper and bead up. When charged, water molecules are attracted to the paper and spread rather than stick. These findings can be applied to ink but studying molecular interactions at the liquid-solid boundary is difficult, because the bulk of the liquid gets in the way.

To study the interface, Pemberton and her team developed a special technique of applying a drop of liquid to the end of a rotating cylinder. As the cylinder rotated, the liquid spread into a thin film only a few molecules thick. By using different energy light beams they could work out how the liquid molecules vibrated and the behaviour of the boundary-layer molecules. The technique is known as emersion and is proving to be the most successful method of understanding solid-liquid interfaces at the molecular level.

Posted 28th April 2004

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