The Discovery of Liquid Crystals

Everyone is familiar with three of the common states of matter solid, liquid and gas. Some substances exhibit all these states as the temperature is varied. For example, water is solid below 0°C, liquid between 0°C and 100°C, and a gas above 100°C. However, this simplified classification is known to be not generally accurate for many materials. Liquid crystals are states of matter which are sometimes observed to occur between the sofid crystal state and the isotropic liquid state. A substance is 

Vorl der, in 1907 [274], discovered that an essential prerequisite for the occurrence of two melting points was a rod-like molecule. This discovery was to be of crucial importance for the theoretical development of Uquid crystals since it allowed theoreticians to mathematically describe fhe molecular structure as rod-like. This rod-like description, together with more advanced descriptions of molecular shapes, remains in use today for modelling many Uquid crystal phases. 

In 1922, Priedel [94] described different liquid crystal phases and proposed a classification scheme consisting of three broad categories called nematic cholesteric and smectic. This classification has since been widely adopted and is now in common usage. 

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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 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. 

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 ... 

SINCE the discovery of liquid crystalline phenomenon for low molecular weight liquid crystals (LMWLCs) more than 100 years ago, anisotropic ordering behaviors of liquid crystals (LCs) have been of considerable interest to academe [1-8], In the 1950s, Hory postulated the lattice model for various problems in LC systems and theoretically predicted the liquid crystallinity for certain polymers [1-3], As predicted by the Hory theory, DuPont scientists synthesized lyotropic LCPs made of rigid wholly aromatic polyamide. Later, Amoco, Eastman-Kodak, and Celanese commercialized a series of thermotropic main-chain LCPs [2]. Thermotropic LCPs have a unique combination of properties from both liquid crystalline and conventional thermoplastic states, such as melt processibility, high mechanical properties, low moisture take-up, and excellent thermal and chemical resistance. Aromatic main-chain LCPs are the most important class of thermotropic LCPs developed for structural applications [2,4-7]. Because they have wide applications in high value-added electronics and composites, both academia and industry have carried out comprehensive research and development. 

After Gerhard Wegner had left Freiburg to become the co-founder and director of the Max Planck Institute for Polymer Research in Mainz, Heino Finkelmann joined the Institute in 1984. In his research, Heino Finkelmann successfully combined the anisotropy of liquid crystals with the viscoelasticity of polymers [26]. This led him to the discovery of new generations of liquid crystalline elastomers, tunable lasers, and stimuli-responsive smart macromolecular materials. 

The publication of density and specific volume studies on mesogens started soon after the discovery of liquid crystalline phases. In 1898/99 and 1905 Schenck [1, 2] reported specific volume data for PAA and p-meth-oxycinnamic acid. Until 1958/1960, with the publication of the Maier-Saupe theory [3], specific volume and density data on mesophases were the topics of only a few publications, and were always combined with results of other measurements [4—15]. A brief historical review of this aspect of liquid crystal research has been given by Bahadur [16],... 

One of the most striking anisotropic properties of nematic liquid crystals is their optical anisotropy, which is manifested as birefringence. It was this property of liquid crystals that led to their discovery about 100 years ago, and early in the history of liquid crystals attempts were made to determine their birefringence. The first rough estimation was made by Lehmann in 1905 [1], who placed the nematic phase of 4,4 -bis(methoxy)azoxybenzene between a plane glass plate and a lens with a large radius of curvature. The birefringence... 

Thermotropic liquid crystals hold a dominant position in the field of the LCD however, researchers have also to pay attention to another type of liquid crystals, lyotropic liquid crystals, fi om the aspect of the life science field. Essential properties of cell membranes originate from their liquid crystalline behavior. The point of view of biophysics exists in the liquid crystal discovery time inferred from the monograph of Otto Lehmaim titled The liquid crystal and life flieory . In the experimental research of material science, the development of science cannot be expected without collaboration with a physicist, a physical chemist, and a synthetic chemist, as showing the history of research not only as that of liquid crystals but also of macromolecules and colloid science, among others. Because a considerable portion of a living organism (cell membrane, skin structure, etc.) is composed of liquid crystalline states, participation of researchers from many different fields is necessary for the bio-matter liquid crystal. I would hope to see the development of medical science, pharmacy, and foods by the full utilization of the potential of liquid crystal materials. 

Over the 100 years since its discovery, liquid crystals have been the intriguing subject for both academia and industries. The textbook of de Gennes "The Physics of Liquid Crystals published in 1974 is still the bible for many LC researchers, but new subjects unmentioned in the book have also risen for these years. This chapter describes the story of the recent developments and the future perspectives in physics of liquid crystals, especially focusing on the contributions by Japanese research groups for the last decade. 

I strongly requested that the early and later researchers should keep in mind, in writing about the development of liquid crystal materials or the related components of the LCD in advances fi-om the electric calculator to the LCD A process and a way of thinking that preceded the invention and/or the discovery , and What brought about the breakthrough in industriahzation of the LCD ... 

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. 

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