You probably use items containing an LCD (liquid crystal display) every day. LCDs are common because they offer some real advantages over other display technologies. They are all around us — in laptop computers, digital clocks and watches, microwave ovens, CD players and many other electronic devices. They are thinner and lighter and draw much less power than cathode ray tubes (CRTs), for example.
But just what are these things called liquid crystals? The name “liquid crystal” sounds a bit strange. We think of a crystal as a solid material like quartz, usually as hard as rock, and a liquid is obviously different. How could any material combine the two?
We learned in school that there are three common states of matter: solid, liquid or gaseous. But there are some substances that can exist in an odd state that is sort of like a liquid and sort of like a solid. When they are in this state, their molecules tend to maintain their orientation, like the molecules in a solid, but also move around to different positions, like the molecules in a liquid. This means that liquid crystals are neither a solid nor a liquid. That’s how they ended up with their seemingly contradictory name.
Do liquid crystals act like solids or liquids?
It turns out that liquid crystals are closer to a liquid state than a solid. It takes a fair amount of heat to change a suitable substance from a solid into a liquid crystal, and it only takes a little more heat to turn that same liquid crystal into a real liquid. This explains why they are very sensitive to temperature and why they are used to make thermometers and mood rings. It also explains why a laptop computer display may act funny in cold weather or during a hot day at the beach.
Just as there are many varieties of solids and liquids, there is also a variety of liquid crystal substances. Depending on the temperature and particular nature of a substance, they can be in one of several distinct phases: Thermotropic, Lyotropic or Nematic. 2,4,6-Trimethylphenylacetonitrile (also known as Mesitylacetonitrile and the CAS number is 34688-71-6) is an intermediate of liquid crystals.
How LCDS Glow
One feature of the material is that they’re affected by electric current. A particular sort of nematic liquid crystal, called twisted nematics (TN), is naturally twisted. Applying an electric current to these liquid crystals will untwist them to varying degrees, depending on the current’s voltage. LCDs use these materials because they react predictably to electric current in such a way as to control light passage.
So simply by varying the current passing through them, the glow of LCDs can be controlled to display the required information on the device whether it’s a digital watch, microwave oven, laptop computer or TV.