Editing Electronic paper (section)

===Electrowetting===
{{Main|Electrowetting}}
'''Electrowetting display''' ('''EWD''') is based on controlling the shape of a confined water/oil interface by an applied voltage. With no voltage applied, the (colored) oil forms a flat film between the water and a hydrophobic (water-repellent) insulating coating of an electrode, resulting in a colored pixel. When a voltage is applied between the electrode and the water, the interfacial tension between the water and the coating changes. As a result, the stacked state is no longer stable, causing the water to move the oil aside. This makes a partly transparent pixel, or, if a reflective white surface is under the switchable element, a white pixel. Because of the small pixel size, the user only experiences the average reflection, which provides a high-brightness, high-contrast switchable element.

Displays based on [[electrowetting]] provide several attractive features. The switching between white and colored reflection is fast enough to display video content.<ref>{{citation |last=Zyga |first=Lisa |date=26 July 2010 |title=Oil-based color pixels could let you watch videos on e-paper |url=https://phys.org/news/2010-07-oil-based-pixels-videos-e-paper.html |newspaper=PhysOrg |access-date=20 November 2011 |archive-date=15 October 2015 |archive-url=https://web.archive.org/web/20151015221450/http://phys.org/news/2010-07-oil-based-pixels-videos-e-paper.html |url-status=live }}</ref> It is a low-power, low-voltage technology, and displays based on the effect can be made flat and thin. The reflectivity and contrast are better than or equal to other reflective display types and approach the visual qualities of paper. In addition, the technology offers a unique path toward high-brightness full-color displays, leading to displays that are four times brighter than reflective LCDs and twice as bright as other emerging technologies.<ref>LiquaVista electrowetting display technologies http://www.liquavista.com {{Webarchive|url=https://web.archive.org/web/20191102144309/https://www.liquavista.com/ |date=2019-11-02 }}</ref> Instead of using red, green, and blue (RGB) filters or alternating segments of the three primary colors, which effectively result in only one-third of the display reflecting light in the desired color, electrowetting allows for a system in which one sub-pixel can switch two different colors independently.

This results in the availability of two-thirds of the display area to reflect light in any desired color. This is achieved by building up a pixel with a stack of two independently controllable colored oil films plus a color filter.

The colors are [[CMYK color model|cyan, magenta, and yellow]], which is a subtractive system, comparable to the principle used in inkjet printing. Compared to LCD, brightness is gained because no polarisers are required.<ref>{{cite web |url=http://www.hinduonnet.com/seta/2003/10/02/stories/2003100200060200.htm |date=October 2, 2003 |title=The Hindu: Technology for reflective full-color display |access-date=2018-11-30 |archive-url=https://web.archive.org/web/20110309052402/http://www.hinduonnet.com/seta/2003/10/02/stories/2003100200060200.htm |archive-date=2011-03-09 |url-status=usurped }}</ref>

====Electrofluidic====
'''Electrofluidic display''' is a variation of an electrowetting display that place an aqueous pigment dispersion inside a tiny reservoir. The reservoir comprises less than 5-10% of the viewable pixel area and therefore the pigment is substantially hidden from view.<ref>{{cite web|title=Gamma Dynamic Technology|url=http://gammadynamics.net/technology/|publisher=Gamma Dynamics|access-date=1 April 2012|archive-url=https://web.archive.org/web/20120303154148/http://gammadynamics.net/technology/|archive-date=3 March 2012|url-status=dead|df=dmy-all}}</ref> Voltage is used to electromechanically pull the pigment out of the reservoir and spread it as a film directly behind the viewing substrate. As a result, the display takes on color and brightness similar to that of conventional pigments printed on paper. When voltage is removed liquid surface tension causes the pigment dispersion to rapidly recoil into the reservoir. The technology can potentially provide greater than 85% white state reflectance for electronic paper.<ref>{{cite journal| title = May 2009 issue of Nature Photonics| journal = Nature Photonics| date = May 2009| volume = 3| issue = 5| pages = 304| doi = 10.1038/nphoton.2009.66| last1 = Graydon| first1 = Oliver| doi-access = free}}</ref>

The core technology was invented at the Novel Devices Laboratory at the [[University of Cincinnati]] and there are working prototypes developed by collaboration with [[Sun Chemical]], [[Polymer Vision]] and Gamma Dynamics.<ref>{{Cite web|url=http://www.gammadynamics.net/|title=gammadynamics.net|website=www.gammadynamics.net|access-date=2009-04-22|archive-date=2009-05-02|archive-url=https://web.archive.org/web/20090502144448/http://www.gammadynamics.net/|url-status=live}}</ref><ref>{{cite web |url=https://www.usnews.com/articles/science/2009/05/04/make-brighter-full-color-electronic-readers--brilliant.html |title=Make Brighter, Full-Color Electronic Readers? — Brilliant! |date=2009-05-09 |work=US News }}</ref>

It has a wide margin in critical aspects such as [[brightness]], [[color saturation]] and [[Response time (technology)#Display technologies|response time]].
Because the optically active layer can be less than 15 micrometres thick, there is strong potential for [[rollable display]]s.