Applications of Liquid Crystals
In 1911, C. Mauguin discovered and described the Twisted Nematic structure. This configuration would play a crucial role in display research more than sixty years later. Before the explosion of liquid crystal display applications happened in the 1960’s, much research on the electro-optical properties of liquid crystals took place in France, Germany, the U.S.S.R, and Great Britain. Perhaps the most important step toward liquid crystal applications was the discovery of the transistor. In particular, the thin film transistor (TFT), patented by J.E. Lilienfield in 1925, would be used in conjunction with the twisted nematic structure for display applications in the eighties and nineties, proving itself to be a valuable technical advance [6].

Despite such early developments, the first true application of liquid crystals was not patented until 1936, when researchers at the Marconi Wireless Telegraph company developed a liquid crystal light valve. In the 1950’s, the application of cholesteric liquid crystals as temperature sensors was developed at Westinghouse research laboratories.

Another obstacle to the development of applications was the lack of liquid crystal compounds that were stable at room temperature. The synthesis of MBBA, which was nematic at room temperature, was a significant step to correct this problem. In addition to this and the development of mixtures of liquid crystals by the RCA group, a major breakthrough came when George W. Gray introduced cyanobiphenyl liquid crystals to the scientific community in 1973. These materials were stable over a large temperature range, and proved excellent both for displays and for basic research. These and other developments led the TN LCD to be the center of the multimillion dollar international flat panel industry we enjoy today.

George W. Gray

It is appropriate to note here the significance of Dr. Gray’s book, Molecular Structure and Properties of Liquid Crystals, published in 1962. This was the first book in English covering the subject of liquid crystals. Before this publication, liquid crystals did not appear in Physics or Chemistry curricula in most universities. Now, many books on the subject of Condensed Matter Physics contain sections on Liquid Crystals.

As the electrical and optical properties of stable room-temperature nematic materials became well known, scientists began investigating the possibility of building optical devices. Heilmeier is credited with being the first to consider liquid crystals for display purposes. In the 1960’s, he developed guest-host displays, and in 1968 watches were built using his Dynamic Scattering Effect.

Early liquid crystal displays required high voltages in order to switch, and suffered from poor contrast ratios. The Twisted Nematic Field Effect Display, patented

James Fergason

in 1969 by James Fergason, who was working at Kent State University, was the first commercially successful display used in pocket calculators and wrist watches, and later in small TV’s and laptop computers. Wolfgang Helfrich and Martin Schadt of Hoffman La-Rouche in Switzerland published a paper on the same subject in 1970[7]. This display had the good fortune of being invented at the time the electronics industry was first developing inexpensive integrated circuits. The combination of these two components yielded very effective affordable digital display devices.

Following the great amount of research into material properties in the 1970’s, researchers were ready to look at other possibilities for displays. In 1980, six years after the discovery of Ferroelectric liquid crystals, Noel Clark from the United States and Sven Lagerwall from Sweden developed the Surface Stabilized Ferroelectric Liquid Crystal display (SSFLC), using chiral smectic liquid crystals.

Noel Clark Sven Lagerwall

This was the first electronic display to exhibit bistability. Also, its switching speed is faster than any other LC display invented so far.

Observations that the electro-optic curves of TN devices were not steep enough to promote multiplexing led Terry Scheffer to develop the first Super Twisted Nematic displays, his Supertwisted Birefringent Effect (SBE) displays, in 1984. The OMI, an achromatic modification of the SBE device developed by M. Schadt in 1987, is widely used in laptop displays today.

J. W. Doane

In 1986, J. W. Doane and others developed Polymer Dispersed Liquid Crystal (PDLC) displays, which could operate without polarizers[8]. A large number of other clever displays techniques using cholesteric, antiferroelectric, absorptive, and other liquid crystalline properties have since been proposed and developed by researchers in many countries.