Physics 2000 Einstein's Legacy Laptop Screens

Liquid Crystals

I'll begin at the beginning, by explaining just what a liquid crystal is: it's a substance that behaves something like a liquid and something like a solid. If you were to touch the stuff, it would feel gooey and soapy--in fact, the slimy mess you find at the bottom of a soap dish is a genuine liquid crystal, not much different from the material in a laptop screen.

Vivid description--but I don't quite understand how something could be like a liquid and a solid at the same time. Well, can you explain the difference between a liquid and a solid, in terms of how their molecules behave?

Sure. In a liquid, the molecules are all sort of sloshing around randomly, with no fixed positions. In a solid, the molecules are pretty rigidly attached to each other, and (at least in most solids) there's some kind of regular structure, some pattern in which they're arranged.

That's exactly right. The term "crystal" refers to materials that have that kind of ordered structure. Now, in a liquid crystal, as in an ordinary liquid, the positions of the molecules aren't very orderly at all.

All right...so where does the crystal part come in?

What makes a liquid crystal different from ordinary liquids is the shape of its molecules: they're long and thin, like french fries. Even if the molecules' positions are random, their orientations can be aligned with one another in a regular pattern--and that's what creates the ordered structure of a liquid crystal.



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