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Each "pixel" in this display is a sealed container of thick shatter-proof glass. It contains salt water, pH indicator, two electrodes, and a small spark plug.
To activate a pixel, current is applied across the electrodes. This will electrolyze the brine and change the pH of the solution:
2NaCl(aq)
==> H2(g)+Cl2(g) + 2NaOH (aq)
This will cause the indicator change colors (e.g., phenolpthalein turns purple when acidic, etc.)
Here's the fun part: To reset, the spark-plug (which is at the top of our chamber, and thus dry) is activated, causing the hydrogen and chlorine to react with each other (giving off light and sound):
H2(g) + Cl2(g) ==> 2HCl(g)
The gaseous hydrogen chloride then dissolves in the NaOH solution and yields:
HCl(aq) + NaOH(aq) ==> NaCl(aq) +H20(l)
This will restore the pH to neutral and re-set the original color of our "pixel"
WARNING: do NOT try this at home. A much simpler version might be an array of beakers filled with salt water (under a fume hood, of course). The "re-set" can be done with a little bit of HCl.
How Squid do it.
http://www.mbl.edu/...o/squid/skin.0.html
Oddly, they perform mechanically, rather than chemically. [zen_tom, Nov 01 2006]
Like Liquid Crystal Jelly?
Liquid_20Crystals_20Jelly_20(Jello)
(Except these are thermal- Which I guess could be caused by an electric current) [Dub, Nov 03 2006]
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Annotation:
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Instead of a spark plug, a laser might work? I suppose the electrodes could be continuously changing the solution of every pixel (so only a simple common system is required), and the laser is resetting often or not often depending on the amount of colour that is required at each point.
Taking that thought even further, if the electrolyte was encased between two flat sheets of glass, which had conductive inner surfaces, then the solution between could be continuously changed by electrolysis, and local areas could be reset by a laser. Different layers could be sandwiched together for different colours.
Voxel: Astra way to do it. |
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Actually, what I'm really wondering is whether there's a reversible (and electrochemically driven) reaction that would accomplish the same thing (color change) |
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Although the spark plugs would definitely add a 'coolness' factor, that would be a more elegant solution... |
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The "refresh rate" of this system would not be fast at all, whether you used a laser or a spark plug. (With a laser, you'd need something light-absorbing to aim at inside the cell). |
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