The Nobel Prize in Physics 1991
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Liquid crystals 
| Digital watches, calculators,
flat TV-displays, thermometers which show the body
temperature in colour, and computers with fantastic
colour graphics are all examples of what liquid
crystal technology can achieve. Liquid crystals are partly ordered anisotropic materials. They are ordered differently in different directions and the order can be steered by electric, magnetic or mechanical signals. For example, weak electric fields can be used to align the molecules, and therefore the polarisation of light passing through the material, very precisely. If the incoming light is already polarized one can use the field to control whether light is transmitted or not. In this way one can create pictures, letters and numerals. This is the idea behind displays in watches, calculators and TV-screens. Liquid crystals consist of elongated organic molecules, generally 3-5 nm long. In the figure below an example is shown together with the different phases such molecules form at different temperatures. |
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| Photo: L. Falk | MBBA molecule. With hydrocarbon chains attached, such molecules can give rise to a number of different phases according to the temperature. |
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| A smectic crystal viewed through
a polarisation microscope. |
Nematic "droplets" with the direction of molecular orientation marked. | A liquid of nematic "droplets" viewed through a polarisation microscope. Different layers correspond to different molecular directions. |
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Liquid crystal historyA transition, which occurred in several distinct steps from the ordered crystalline phase to the disordered liquid phase, was first noted in a cholesterol related substance by the botanist F. Reinitzer in 1888. Soon after the physicist O. Lehmann showed that these steps were thermodynamically distinct phases. He named them liquid crystals. Experimental investigations by Lehmann and the mineralogist G. Friedel, together with the theory of liquid crystals presented by the physicist C.-W. Oseen, formed the scientific bases of this new field of research. It was not until in the 1950s that further progress was made in understanding liquid crystals (by F.C. Frank and others). Since mid 1960 the entire theoretical and experimental development has been influenced by Pierre-Gilles de Gennes.
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