Twisted nematic field effect
The twisted nematic effect (TN-effect) was a major technological breakthrough that made the manufacture of large, thin liquid crystal displays practical and cost competitive.
The twisted nematic effect is based on the precisely controlled realignment of liquid crystal molecules between different ordered molecular configurations under the action of an applied electric field.
The underlying phenomenon of alignment of liquid crystal molecules in applied field is called Fréedericksz transition and was discovered by Russian physicist Vsevolod Frederiks in 1927.
Because of this, voltage-controlled addressing of matrix displays, such as in LCD-screens for computer monitors or flat television screens, is more complex than with segmented electrodes.
Aware of the long line of research involving nematic liquid crystals, he started experimenting with the compound p-azoxyanisole which has a melting point of 115 °C (239 °F).
Williams set up his experiments on a heated microscope stage, placing samples between transparent tin-oxide electrodes on glass plates held at 125 °C (257 °F).
In 1964, RCA's George H. Heilmeier along with Louis Zanoni and chemist Lucian Barton discovered that certain liquid crystals could be switched between a transparent state and a highly scattering opaque one with the application of electric current.
By placing a reflector on the far side of the crystal, the incident light could be turned on or off electrically, creating what Heilmeier dubbed dynamic scattering.
Not being self-lit, LCDs also required external lighting if they were going to be used in low-light situations, which made existing display technologies even more unattractive in overall power terms.
However RCA showed little interest because they felt that any effect that used two polarizers would also have a large amount of light absorption, requiring it to be brightly lit.
In 1970, Helfrich left RCA and joined the Central Research Laboratories of Hoffmann-LaRoche in Switzerland, where he teamed up with Martin Schadt, a solid-state physicist.
Schadt built a sample with electrodes and a twisted version of a liquid-crystal material called PEBAB (p-ethoxybenzylidene-p'-aminobenzonitrile), which Helfrich had reported in prior studies at RCA, as part of their guest-host experiments.
[4] When voltage is applied, PEBAB aligns itself along the field, breaking the twisting structure and the redirection of the polarization, making the cell turn opaque.
At this time Brown, Boveri & Cie (BBC) was also working with the devices as part of a prior joint medical research agreement with Hoffmann-LaRoche.
Fergason was working on the TN-effect for displays, having formed ILIXCO to commercialize developments of the research being carried out in conjunction with Sardari Arora and Alfred Saupe at Kent State University's Liquid Crystal Institute.
This work, in turn, led to the discovery of an entirely different class of nematic crystals by Ludwig Pohl, Rudolf Eidenschink and their colleagues at Merck KGaA in Darmstadt, called cyanophenylcyclohexanes.
