Why do LCD displays fade to black when powered by DC instead of AC?

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i have a few questions:

1)what is the liquid used?

2)is the glass etched inside to hold the liquid or do they use a thin film of two layers, one conducting?

3)lcds use 180hz square waves to keep the display liquid black, but when just using dc the display will turn black and then fade, why?
 
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Here's a reasonably good starting point:

http://en.wikipedia.org/wiki/Liquid_crystal_display

Many different materials and techniques are used for LCDs. In general, though, most use variations in the electric field across a pixel cell to alter the way that light's polarization is affected when going through the cell. So yes, there are clear conductor stips on the inside surfaces of the glass plates, and AC waveforms are used to affect the liquid crystal molecules inside each pixel cell.
 
BTW, is this a homework problem? If so, I can move it to the homework forums.