From rigid-rods to main-chain polymers

In March 1888, a young botanist called Friedrich Reinitzer wrote to Otto Lehmann who was professor of physics at Aachen. He described observations, published that year (Reinitzer, 1888), that esters of cholesterol appeared to have two melting points between which the liquid showed iridescent colours and birefringence. It was sensible to consult Lehmann as he had worked for some time in the field of crystal transitions and, above all, had developed a polarising microscope with a hot stage, which was to become a central feature of much of his research. He confirmed Reinitzer's observations, and postal collaboration between the two over the next few years laid the foundations of liquid crystal science. By 1889, Lehmann was describing the material as ‘flowing crystals’ and the following year as ‘crystalline liquids’ (Lehmann, 1889, 1890). From this point onwards, he was making most of the running and gradually became the hub of a wider collaboration. He spread interest beyond Germany, notably to France and Holland. Liquid crystal science continued to mature and synthetic chemists, in particular Vorländer at Halle, demonstrated the principles of molecular design which underpin the field. There was considerable debate between George Friedel, working in Strasbourg, and Lehmann and Vorländer, as to the existence of different types of liquid crystalline phase. However, the issue eventually reduced to one of semantics, as it was recognised that liquid crystallinity does indeed appear in several different guises.