Otto Lehmann (physicist)
Otto Lehmann ( born January 13 1855 in Konstanz, † June 17, 1922 in Karlsruhe ) was a German physicist and spiritual father of the liquid crystal research.
Life-history
Lehmann studied 1872-1877 Natural Sciences at the University of Strasbourg and then his doctorate at Paul Heinrich von Groth, the founder of the Journal of Mineralogy and Crystallography (1877 ), on physical isomerism (Isomers are molecules of the same molecular formula but different structures ). First, he was a teacher of physics, mathematics and chemistry at the secondary school in Mulhouse in Alsace prior to October 1, 1883 as a lecturer in physics at the then Royal. Technische Hochschule in Aachen was hired. 1888 Lehmann was appointed as professor of electrical engineering at the Royal. Saxon Polytechnic appointed to Dresden. But a year later he succeeded Heinrich Hertz at the Physical Institute of the Technical University of Karlsruhe with teaching of physics and electrical engineering. This university, the rector of which he was in the years 1900 and 1901, he remained connected until his death in 1922. After 1912 Lehmann was repeatedly nominated for the Nobel Prize, but without ever receive it.
His son Karl Otto (1903-1976) studied electrical engineering in Karlsruhe and later became a professor there also.
Liquid crystals
Lehmann's academic life's work can be collectively described by the title of his 1904 published in Leipzig main station: Liquid crystals. Since the 70s of the 19th century Lehmann systematically investigated crystal growth and changes in modification of crystalline substances. He uses, among others, one of him in 1877 and developed in 1884 and 1890 improved crystallization microscope. This microscope he also employs to study the internal structure of bodies. His 1888/89, published in Leipzig molecular physics summarizes the entire former knowledge of the physics of matter together. So Lehmann points to some, " that if you go out with the pressure acting on a rigid body forces beyond the elastic limit, the form of changes in the body occur, which is similar view as essentially overcoming the rigidity than a slow flow of the liquid flow can. "He had already in 1877 observed that " has viscous modification of silver iodide may octahedral shape. "
1888 reported the Austrian botanist and chemist Friedrich Reinitzer ( 1857-1927 ) of the German Technical University in Prague that he had observed magnificent color phenomena and the simultaneous occurrence of crystals and amorphous fused mass on heating and subsequent cooling of two substances in polarized light. Reinitzer cholesterol benzoate had discovered and found that this strange substance melts at 145 ° C, but only at temperatures above 179 ° C. to a clear liquid. At temperatures above 145 ° C and 179 ° C, the fabric looks milky cloudy. Lehmann examined these Reinitzerschen so-called preparations and realized that cholesterol benzoate and he examined Iodide between the liquid and solid even have a third phase and show in this intermediate phase identical behavior, such as a strong birefringence under the polarizing microscope. Lehmann begins with the systematic analysis of the substances and place in the sequence more than 100 substances with similar behavior. Lehmann called these substances " flowing crystals ".
1891 Lehmann founded his namesake crystal analysis. Comparing a known compound to be tested with the identical characteristics. He uses the crystallization microscope constructed by him. According to Lehmann, crystalline amorphous bodies differ in that amorphous bodies have no growth direction. 1904 Lehmann published a summary of his findings his work Liquid crystals. Until his death in 1922, the liquid crystals remained central theme of his research. Otto Lehmann left with this issue once and for that time almost completely unexplored chapter of physics. But a technical application for the phenomena he discovered there was not at first. Thus came the " liquid crystals " and its discoverer for nearly sixty years more or less forgotten.
LCD
It was not until the late sixties began again to deal intensively with Lehmann's liquid crystals. In 1971, the Swiss chemical company F. Hoffmann -La Roche first prototypes of liquid crystal displays according to the principle of the nematic twist cell (LCD = Liquid Crystal Display ) with organic liquid crystals ago ( Schadt -Helfrich cell, for details of Gerhard H. Buntz: Twisted Nematic Liquid Crystal Displays ( TNLCDs ) - An invention from Basel goes around the world ). Liquid crystals are characterized by the fact that within a temperature range (about -20 ° C to 70 ° C ) is given between the normal liquid and the solid phase, a liquid state in which the molecules of these substances in at least one spatial direction ( nematic phase) or in addition orient uniformly in layers ( smectic or cholesteric phase). The individual layers are displaced against each other and in and rotate. The totality of these phases between isotropic liquid and the solid is called mesophase. As in a crystal leads the order of molecules here optical effects ( birefringence polarization of the light, etc.), the LCD is affected by applying electric fields, the molecular structure in the mesophase so that the refraction of the liquid crystal changes reversibly, that is, the liquid crystal after switching off the electric field returns to its original state. Visually, this behavior does in polarized light, for example, as the brightness contrast, thereby providing an indication of numbers or letters is possible. Advantage of the liquid crystal display is the extremely low electric power in the range of a few uW / cm ², which is needed for operating such a display. After you had achieved by the Active - matrix addressing the problems arising ( lower contrast, reduced Sehrichtungsbereich, long response times, for example ) due to the electrical activation in so-called " passive - matrix displays ," appeared liquid crystal displays mid-1970s for the first time in digital watches on as a technical application. They are now widely used in all kinds of technical applications. They are inexpensive and require virtually no power. After the way they produce their respective images or pixel ( = picture elements), a distinction is made between TN ( Twisted Nematic = ) -, STN ( Super Twisted Nematic = ) -, D- STN ( Super Twisted Nematic = Double ) - displays, or so-called TFT ( = Thin Film Transistor) display. In TFT - LCDs, each pixel is controlled by its own transistor.
Otto Lehmann Foundation
Since 1998, gives an Otto Lehmann Foundation a named after the famous physicist Award for the promotion of scientific works of young professionals in the field of liquid crystal display. The triumph and the proliferation of portable computers in notebook format with liquid crystal display and the fact that today manages hardly a machine, an electrical appliance or industrial use without an LCD, is the most striking proof of the enormous technical and economic importance of the discoveries Otto Lehmann.
Works
- Self -made physical apparatus. Leipzig 1885.
- Molecular physics. 2 vols, Leipzig 1888/89.
- The crystal analysis. Leipzig 1891.
- Electricity and light. Braunschweig 1895.
- Liquid crystals. Leipzig 1904.
- The seemingly living crystals. Esslingen in 1907.
- The main concepts and laws of physics. Berlin, 1907.
- The crystallization microscope and the discoveries thus made particularly that of the liquid crystals. From the Festschrift of Fridericiana the 53rd birthdays His Royal. Highness the Grand Duke Frederick II of Baden. Vieweg, Braunschweig, 1910.
- Liquid crystals and their apparent life. Research results presented in a movie. Voss, Leipzig 1921.