Discovery of liquid crystals

The discovery of liquid crystals by humans is due to the Austrian botanist Friedrich Reinitzer [14] what he observed in 1888 were cholesteric MLCs (see Section 41.3.1). Some people did not believe Reinitzer that such strange structures are possible. However, a German scientist named Otto Lehmann asked Reinitzer for some samples, conducted similar experiments, and reported virtually identical results a year later [15]. Given the popirlar disbelief, Lehmaim s resirlts were not exactly trivial. Lehmaim also coined the name liquid crystals —over objections of Reinitzer, who said the name is wrong and constitutes a contradiction. As you can easily imagine, there were cen-tennnial celebrations in Austria in 1988 and in Germany in 1989. 

The discovery of liquid crystals was made by Friedrich Reinitzer while working with the compound cholesteryl benzoate. In the time since its discovery, thousands of other organic compounds have been found to have a liquid crystal state. 

Since the discovery of liquid crystals more than 100 years have passed. For the first time, they were revealed by the Austrian botanist Reinitzer (1888), who observed a peculiar thermal behavior of cholesteryl benzoate ester. ... 

The polarizing light microscopy is the simplest method available to identify LC phases. This optical method has been used since the discovery of liquid crystals and has led to nematic, cholesteric and smectic classifications. The appearance of a specific texture of the melt is usually a function of the types of LC phase, and it is often possible to directly identify the type of LC phase present in a polymer melt by this optical method. The textures of various LC phases are caused by the existence of different types of defect present in the LC phases. It should be noted that microscopic observations are sometimes misleading because the development of specific textures in an LC phase can occur with great difficulty. This problem arises owing to their multiphase nature (the coexistence of polycrystalline and amorphous phases), polydispersity and/or higher viscosities of LCPs melts compared with those of LMLCs. In most cases, LCPs must be annealed for hours or days at suitable temperatures to develop specific textures. 

This period of history also saw the publication of work by Eaborn and Hartshome [32] on di-isobutylsilandiol, which generated a mesophase. This was a puzzling result at the time, as the molecular shape was inconsistent with views of the time that liquid crystal formation required rod-shaped molecules. Light would be shed on this only after the discovery of liquid crystal phases formed by disc-shaped molecules in the early 1970s. 

Traditionally, the discovery of liquid crystals has been attributed to Friedrich Reinitzer in 1888. Reinitzer was a scientist at the German University of Prague in the Institute of Plant Physiology while studying the properties of cholesterol compounds, he found that cholesterol benzoate appeared to have two different melting points. Another scientist of the time, Otto Lehman, a crystallographer at the University of Aachen, first proposed the liquid crystal state to be a distinct new state of matter. ... 

The first scientific description of liquid crystals was provided by the Austrian botanist Friedrich Reinitzer. This was in 1888, hence in 1988 we had celebrations of 100 years of discovery of liquid crystals. We also had celebrations in 1989, because in 1889 the German scientist Otto Lehmann coined the name liquid crystals . Lehmann confirmed the experimental results of Reinitzer, which was important, since some people did not believe Reinitzer. However, Reinitzer was not exactly grateful he maintained that the name liquid crystals is wrong and constitutes a contradiction. 

Reinitzer, F. Beitrage zur Kenntnis des Cholesterins , Monatsh. 9, 421, 1888. The term liquid crystals was first used by O. Lehmann in Fluessige Kristalle . Engelmann, Leipzig, 1904. See also H. Kelker, History of liquid crystals. Mol. Cryst. Liq, Cryst. 21, 1 (1973). For a history of the discovery and recognition of plastic crystals see J. Timmermanns, Plastic crystals, a historical review. J. Phys. Chem. Solids 18,1 (1961)... 

The first ideas on the nature of liquid crystals in hpids were derived from X-ray studies by Luzzati [1]. A crucial discovery was his demonstration of the liquid character of the hydrocarbon chains, which are thus space-filling. This was evident after it was foimd that the Upid bilayer thickness decreases with temperature with a large linear thermal coefficient about 10"3/°C. Such an effect is consistent only with a highly disordered chain conformation. Also the X-ray scattering characteristics were found to be very similar to those of liquid paraffins. 

It is considered that liquid crystals that are soft and have long-distance order may form certain complex hierarchical structures other than blue phases. In fact, recent discoveries of new liquid crystal phases have arisen one after another. While many think of liquid crystals as display materials with the range of applications seemingly exhausted, it is more likely that applications other than displays are only beginning to appear. 

Liquid crystals are broadly classified as nematic, cholesteric and smectic (I)- There are at least nine distinct smectic polytypes bearing the rather mundane labels smectic A, B, C,... I, by the chronological order of their discovery. Some of the smectics are actually three-dimensional solids and not distinct liquid-crystal phases at all. There are three t s of liquid crystals. Thermotropic liquid-crystal phases are those observed in pure compounds or homogeneous mixtures as the temperature is changed they are conventionally classified into nematic, cholesteric, and smectic phases in Fig.2. Lyotropic liquid-crystal phases are observed when amphiphilic molecules, such as soaps, are dissolved in a suitable solvent, usually water. Solutions of polymers also exhibit liquid-crystalline order, the polymeric phases. Most of our knowledge about liquid crystals is based on the thermotropic phases and much of this understanding can be transferred to elucidate polymeric and lyotropic phases. 

Helpful tools for this structurization of liquid crystal research were temperature dependent X-ray investigations [36] of natural and synthetic lipids, and the discovery that mesophases may be identified by their different textures appearing in the microscope using crossed polarizers [37]. In the decade starting in about 1957 systematic screening of the concentration and temperature dependency of the major lyotropic mesophases was done and models of the molecular arrangement in the different phases were developed [38-45] (e.g., the so-called middle or neat phases [38], the cholesteric phase of polypeptides and nucleopep-tides [44]). 

The dualities of supramolecular biomeso-genic organizations [7, 17, 18] reemerge in the process of their scientific discovery. The history of liquid crystals , lovingly retraced by Kelker [13] (Fig. 5), parallels the development of molecular biology [5 - 8]. Liquid crystals are beautiful and mysterious, I am fond of them for both reasons , states de Gennes [19]. And, indeed, how can we not feel attracted to what in the inanimate world seems most closely related to us ... 

Liquid crystals were discovered by the botanist Friedieh Reinitzer, although the first observation of liquid crystals can be likely ascribed to George-Luis LeClerc. After their discovery, liquid crystals were considered for a long time as a curiosity. 

The sensitivity of deuteron NMR to the molecular orientational order and to director field configurations turned out to be extremely useful in studies of liquid crystals confined into snbmicrometer pores. Moreover, the large surface-to-volume ratio of these composite systems render the interfacial and surface phenomena, induced by the liquid crystal-surface interactions, accessible even to an essentially integrative technique like NMR. Since the discovery of polymer dispersed liquid crystals (PDLCs) in 1986 [4], NMR of selectively deuterated liquid crystals was used to discriminate unambiguously among various director structures in cavities, resulting from an interplay between elastic forces, morphology and size of the cavity, and surface interactions. These structures include the escaped-radial, planar axial, planar-polar, and... 

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