Liquid Crystals: The Story Behind the Technology
Did you know that liquid crystals were discovered by a botanist studying carrots?Liquid crystals, most commonly known today for their presence in liquid crystal displays (LCDs), have a molecular makeup somewhere in between a solid and a liquid. Unlike a solid, their molecules are not ordered, but unlike a liquid they do follow some structure. Enter the fascinating world of liquid crystals.
Liquid crystals were accidentally discovered in 1888 by Austrian botanist Friedrich Reinitzer while he studied cholesteryl benzoate of carrots. Reinitzer observed that when he heated cholesteryl benzoate it had two melting points. Initially, at 294°F (145°C), it melted and turned into a cloudy fluid. When it reached 353°F (179°C), it changed again, but this time into a clear liquid. He also observed two other characteristics of the substance; it reflected polarized light and could also rotate the polarization direction of light.
Surprised by his findings, Reinitzer sought help from German physicist Otto Lehmann. When Lehmann studied the cloudy fluid under a microscope, he saw crystallites. He noted that the cloudy phase flowed like a liquid, but that there were other characteristics, such as a rod-like molecular structure that was somewhat ordered, that convinced Lehmann that the substance was a solid. Lehmann continued to study cholesteryl benzoate and other related materials. He concluded the cloudy fluid represented a newly discovered phase of matter and called it liquid crystal.
In nature, liquid crystals aren't only found in plants, most carbon compounds contain liquid crystals. They are found in the shells of beetles, DNA molecules, human bone, wood cellulose and even slug slime.
In the early 1960s chemist Richard Williams began to research the use of liquid crystals while he worked for RCA Laboratories. He discovered that when an electric field was applied to a thin layer of liquid crystals, the crystals would form stripe patterns and enter into a nematic state. His discovery would come to be known as "Williams' domain" and led to the possibly of liquid crystal use in display devices.
A nematic liquid crystal causes the polarization of light waves to change as the waves pass through it, the extent of which depends upon the intensity of the electrical field. One problem Williams encountered while he attempted to use liquid crystals for displays was that in order for liquid crystals to enter a nematic state, they needed to be heated to a temperature impractical for consumer use.
William's colleague, George H. Heilmeier, led a team of two additional research chemists at RCA, Joel E. Goldmacher and Joseph A. Castellano. They discovered that altering the number of carbon atoms allowed for the presence of nematic liquid crystals at room temperature. Their research led to the first liquid crystal displays.
Early LCDs employed dynamic scattering method, or DSM, where an applied electrical charge rearranges liquid crystal molecules so scattered light passes through them. In 1969, RCA announced the first liquid crystal display products which included animated advertising displays, a reduced glare rearview mirror and a gasoline pump readout, but the technology also inspired innovation in several other industries.
In 1960, after nearly a decade of studying the thermal expansion of liquid crystals, James Fergason and two colleagues from Westinghouse Electric Corporation applied for several US patents involving liquid crystals. Fergason and his colleagues proved that a film of liquid crystals exhibited different temperature patterns on the skin. Their research led to the presence of liquid crystals in optical imaging devices, technology still used today. Fergason later had his own company, the International Liquid Crystal Company, release several LCD products, including the first LCD watch.
Besides their use in displays and optical imaging, liquid crystals are used in liquid crystal thermometers, nondestructive mechanical testing, color electronic slides in computer-aided drawing and for visualizing radio frequency wavelengths. A myriad of additional technologies utilizing liquid crystals are still being developed today.