Liquid Crystals are unique partially ordered materials which combine the properties of fluids with the anisotropy of solids. The development of these materials had a profound impact on technology and society in the second part of the 20th and the beginning of the 21st century. Nowadays, it is difficult to imagine the aspects of life where liquid crystals are not involved. However, at the end of the 19th century, mere existence of this state of matter was questionable and led to much disagreement among the scientists. Intensive studies involving interdisciplinary research from all over the world eventually lead to the establishment of liquid crystals or “crystals which flow” and opened doors for their numerous applications [1].
In the early days of liquid crystal research, German scientists made pioneering contributions to the emerging field of liquid crystal science. Intensive research on liquid crystals was initiated by the observation of a "double melting" in cholesteryl benzoate prepared from carrots [2]. This observation was made in 1888 by Friedrich Reinitzer, a professor at the Institute of Plant Physiology at the German University of Prague [3]. He found that cholesteryl benzoate first melted into a cloudy liquid at 145.5°C and the cloudy liquid became clear on further heating at 178.9°C. The "meltings" were accompanied by exhibiting dramatic colours.
Otto Lehmann, a professor of physics at the Technical High School in Karlsruhe, developed a microscopy technique which utilises polarisation and a hot stage, which is still in the heart of any liquid crystal laboratory. This allowed him in 1889 to come to the surprising conclusion that the cloudy phase observed by Reinitzer exhibits crystalline properties and flows at the same time. The first synthetic liquid crystal, para-azoxyanisole (PAA) was prepared in Heidelberg by Ludwig Gattermann. He also introduced the term Schlieren texture to describe the appearance of the nematic phase in a polarising microscope. Chemistry and physical chemistry of liquid crystals became a flourishing research area in Germany at the turn of the twentieth century. A liquid crystal research group was established at the University of Halle where it continues until the present day. In 1902, Daniel Vorländer and his students F. Meyer and K. Dahlem synthesised new classes of liquid crystal materials [4]. Even nowadays, Vorländer's collections stored in old cigar boxes are of scientific interest [2]. Horst Sackmann and H. Arnold identified various smectic phases and introduced the notation smectic-A, -B and -C phases in 1959 [5]. The first synthesis of a liquid crystal showing a nematic phase at room temperature was reported in 1969 [6].
Scientists in Germany contributed not only to the chemistry of liquid crystals but also to the theory. Among them are Wilhelm Maier and Alfred Saupe from Halle. The Maier-Saupe theory of nematic liquid crystals [7-9] successfully describes the character of the nematic-isotropic transition. Wolfgang Helfrich developed in 1970 the theoretical concept of the TN-cell, the realisation of which together with Martin Schadt [10] initiated the rapid development of liquid crystal display applications in the late 20th century.
Today, liquid crystals research is a dynamic and fast-developing area of modern science. Commercial production of liquid crystals was established in the chemical company Merck in Darmstadt, which is nowadays one of the largest industrial suppliers of liquid crystals. Various aspects of this research such as synthesis and structure of novel materials, optics and photonics, molecular and thermodynamic properties, applications for sensors, telecommunications and medicine, are conducted by the scientific group members of the German Liquid Crystalline Society.
The roots of German Liquid Crystal Society go back to 1971 when the first Liquid Crystal Workshop (Freiburger Arbeitstagung Flüssigkristalle) was held in Freiburg. The first meeting of this series was organised by Gerhard Meier and Günter Baur and had not more than 30 attendees. However, it initiated a very successful, internationally recognized series of annual meetings held in Freiburg, part of which were later organized by Heino Finkelmann, Gerd Kothe and Gert Strobl. The Society was officially established in 1996, when Horst Stegemeyer contacted the Bunsen Society for Physical Chemistry (DBG) in order to establish a Liquid Crystal Workgroup. On July 28, 1996, the board of DBG officially established the Workgroup. In June 1998, the Liquid Crystal Workgroup was renamed to German Liquid Crystal Society (Deutsche Flüssigkristall-Gesellschaft, DFKG).
Remarks and References
[1] The early history of liquid crystals is very well illustrated in the book “Crystals That Flow: Classic Papers from the History of Liquid Crystals” by Timothy J. Sluckin, David A. Dunmur, and Horst Stegemeyer, CRC Press, Boca Raton, 2004.
[2] Karlsruhe University hosts a permanent exhibition on the history of liquid crystals, entitled “From the carrot to flat panel displays”. The exhibition was assembled by Horst Stegemeyer and Ludwig Pohl.
[3] The building, where Reinitzer performed his research in the late 19th century is located at Husova Street No. 5, see L. Lejček, M. Glogarová, and E. Těšínská: “Commemorative plaque of Prof. Friedrich Reinitzer installed in Prague”, Liquid Crystals Today 26 (3), 66-68 (2017).
[4] In recognition of Daniel Vorländer’s pioneering work, DFKG invites distinguished young researchers to give a ‘Vorländer Lecture’ at the annual German Liquid Crystal Conference.
[5] For a review, see for example H. Sackmann: “Smectic liquid crystals. A historical review”, Liquid Crystals 5(1), 43-55, (1989).
[6] H. Kelker and B. Scheurle: „A Liquid‐crystalline (Nematic) Phase with a Particularly Low Solidification Point”, Angew. Chem. Int. Ed. 81, 884-885 (1969).
[7] W. Maier and A. Saupe: „Eine einfache molekulare Theorie des nematischen kristallinflüssigen Zustandes“, Z. Naturforsch. 13 a, 564–570 (1959).
[8] For a review, see for example G. R. Luckhurst and C. Zannoni: “Why is the Maier–Saupe theory of nematic liquid crystals so successful?”, Nature 267, 412–414 (1977).
[9] In recognition of Alfred Saupe’s pioneering work, the Alfred-Saupe-Foundation and DFKG bestow the Alfred Saupe Prize to distinguished liquid crystal researchers.
[10] M. Schadt and W. Helfrich: “Voltage-dependent optical activity of a twisted nematic liquid crystal”, Appl. Phys. Lett. 18, 127-128 (1971).