History
The physical and chemical characteristic of different derivative of cholesterol was determined in 1888. The credit goes to Friedrich Reinitzer, a physiologist in Botany from Austria, presently serving in Karl-Ferdinands-Universität. Derivatives of cholesterol now classified as a material called as cholesteric liquid crystal. Formerly, scientists have been revealed diverse color effect, obtained by cooling derivative of cholesterol at little higher than the freezing point, but did not related it with a novel observable fact. Reinitzer supposed that change in color of cholesteryl benzoate derivatives is not the major unusual trait (Figure 1).
Figure 1. Structure of cholesteryl benzoate molecule
Reinitzer introduce that the manner in which cholesteryl benzoate melts differs from other compound, bears double melting points. It melts into a cloudy liquid at 144-145 °C, and then it melts again from the hazy liquid to clear fluid at 177-178 °C. This phenomenon is reversible, he wrote to Otto Lehmann on March 14, 1888, seeking help from a physicist. They exchange scientific material and test models. Lehmann observed the intermediary hazy fluid, and report that there is existence of crystallites. Von Zepharovich, colleague of Reinitzer's Viennese, also added that the intermediate “liquid” was crystalline. Reinitzer offered his outcomes, with acknowledgment to Lehmann and von Zepharovich in the meeting at Vienna Chemical Society on May 3, 1888, (Reinitzer & Friedrich, 1888).
Still that moment, Reinitzer has invented and explained three main characters of cholesteric liquid crystal (Otto Lehmann specified this term in 1904): a) Double melting points are existed b) ability to reflect circular polarized light and c) capability to rotate the polarization direction of light.
Reinitzer did not trail studying liquid crystals further, following his accidental discovery. The investigation was sustained by Lehmann, comprehends that he has met a novel observable fact and be in a situation to examine it: he become specialist in the field of crystallography and microscopy during his postdoctoral years. Lehmann initiated an orderly study started from cholesteryl benzoate then followed by associated materials that displays the double melting phenomenon. The facility of hot stage provided in microscope (sample holder in contact with heater) helps to scan the material at high temperature and also make observations in polarized light. Predominantly the crystals observed in microscope persuaded Lehmann that he was came across a frozen material in the intermediate cloudy phase which shows clearly sustained flow. He had published his results in the literature by the end of august 1889 (Lehman, 1889).
After Lehmann, the German chemist Daniel Vorländer continued and extensively prolonged his work up to his retirement in 1935, during his course of study he synthesize number of liquid crystal. While the liquid crystal, was not admired throughout the world among researchers from different region, so the material remained silent for next research with more scientific curiosity (Sluckin et al., 2004).