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The Theme of Current Research in Solids, Liquids, and Gases

The "In Between" State of Matter: The Liquid Crystal

Remember the old days when televisions were heavy, bulky, and ugly? The technology used in those TVs was a cathode ray tube, which has little to do with solids, liquids, or gases so we'll leave it at that. Today's televisions are thin, beautiful, and lightweight. These TVs feature liquid crystal displays (LCDs).9 The most common application of liquid crystal technology is in LCDs but they're really found everywhere: watches, calculators, computer screens, etc.

Image from here.

As the name suggests LCDs are made from liquid crystal technology. Wait a minute. How does that make sense? We already learned that crystals are a form of solid matter, not liquid.

Actually, the liquid crystal is an "in-between" state of matter, which combines some of the ordering properties of solid matter with some of the movement properties of liquid matter. This results in a homogeneous phase with very different properties from traditional solids or liquids.

Particles in a solid crystal are in fixed locations, jiggling around a bit but never moving far because of the strong IMFs holding them together. Particles in a liquid have no assigned placement and instead are free to roam throughout the container in any direction they choose. A liquid crystal is a combination of these two phases. Its molecules are arranged in a particular pattern, but the particles are not confined to fixed locations. This means the material can still flow like a liquid while maintaining some solid characteristics.

Stiff rod-like molecules are most likely to organize into the liquid crystal phase. Initially the substance is a normal crystalline solid with the molecular rods lining up in an organized rigid manner. If heat is applied, however, the crystal begins to melt and the molecules start to move. The molecules leave their original locations, but their movement is constrained by so many neighbors. In essence, the molecules can move but they must move together because they are so jam-packed. What develops is a homogeneous herd of rigid rods.

The liquid crystal phase is fragile. It happens when a crystal does not fully melt, but there is enough heat to disrupt the crystal lattice to release the molecules from their set positions. If too much heat is applied the molecules can begin to break entirely free from the crowd and fully join the liquid phase. As you can see, a careful balance of heat and concentration is needed to maintain the liquid phase.

Liquid crystals are special and important to our favorite technologies. They can conduct electricity as well as transmit and change polarized light. Companies have figured out how to use the special properties of liquid crystals to make really stunning visual displays. Here is one example of liquid crystal technology in action.

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