Monday, 25 March 2013

Surface Tension of Electrowetting Displays

What is Electrowetting?
If you buy an e-reader from Amazon in the near future you may be using a technology where surface tension properties are important.  Amazon is thinking about buying a Samsung division called Liquavista for 100 million dollars.   Liquavista (and some other companies) use a technology for their displays called electrowetting.  This technology involves modifying the surface tension of liquids on a solid surface using a voltage.  When a voltage is applied the hydrophobic surface can be modified making the surface more wettable.  The voltage acts as a switch to make the surface more and less tense or more and less wettable when compared to the solid support.  The electrowetting effect has been defined as "the change in solid-electrolyte contact angle due to an applied potential difference between the solid and the electrolyte".  For reasons not known only a subset of materials are good for electrowetting.  Amorphous fluoropolymers are the best currently.  

How do they use this technology?
Liquavista uses this technology to make an optical switch by contracting a colored oil film electrically.  When no voltage is applied the colored oil forms a continuous film and the color is visible to the user of the display.  When a voltage is applied possibly with the touch of fingertip for touch screen displays the pixel becomes transparent.  The different pixels can then align to show a photograph or video (video is ideal because of the high switching speed and small pixel dimensions).  
Check out this video to see the speed at which it switches.

How is it different from other technology?
This technology is different than LCD (liquid crystal displays) since they use oil rather than a crystal to display color.  One added advantage of the oil displays used by Liquavista are that they require less power likely because they do not need to be continually refreshed.  Also they are in color so this is also different from E-Ink's product (that only use two tones to achieve the Kindle properties).  According to the BBC, using electrowetting technology could allow for devices to be built that run for several days before needing a charge.  So in essence it will have a battery lifetime like the Kindle but a colored picture like the current LCD diplays in the Iphone.  

How to find new materials to use in electrowetting?
Using a high throughput surface tension device (Delta-8) coupled with a high throughput catalyst could really explore finding new materials with the right properties for electrowetting.