Modern materials liquid crystals

In this section we briefly summarize a few modern applications of simulation techniques for the understanding of crystal growth of more complex materials. In principle, liquid crystals and colloids also belong to this class, but since the relative length of their basic elements in units of their diameter is still of order about unity in contrast to polymers, for example, they can be described rather well by the more conventional models and methods as discussed above. 

Modern communication operates independently of time of day or geographical location. It brings people closer, makes life easier, and has changed the working environment profoundly. At the heart of all this sits a product so common that most people do not even think about its presence. Liquid crystals (LCs) are hi-tech chemical materials with unique properties. Without them we would not have Liquid Crystal Displays (LCDs) - lightweight, flat displays that consume little energy. 

Chemists who synthesized cholesterol benzoate about 100 years ago, a routine synthesis of a derivative of a known compound, had no way of knowing that they had opened a route to the creation of innumerable and various devices in which liquid crystals are used. This new state of a material was unexpectedly discovered in the course of studies which were narrowly focused at the preparation of various derivatives from the readily available natural compound cholesterol. Similarly, the epoch of modern chemotherapy originated with the discovery of sulfa drugs , which happened as an absolutely unexpected consequence in a broad investigation aimed at the synthesis of hundreds of most diversified derivatives of aromatic compounds, potentially useful as components of azo dyes. 

Figure 1.4 Modern materials in a variety of applications. A, Specialized steels in bicycles synthetic polymers in clothing and helmets. B, High-tension polymers in synthetic hip joints. C, Medicinal agents in pills. D, Liquid crystal displays in electronic devices.

We also consider several other novel structures that are important in modern materials chemistry. These include dendrimers, liquid crystals, and fullerenes. Although polymers and these other structures are key components of organic materials chemistry, these topics alone do not encompass all of organic materials chemistry. The impact of organic chemistry on materials chemistry is far broader, including but not limited to the control of interactions between surfaces, the construction of nano-devices, and recently the creation of supramolec-ular materials that self-assemble. You should appreciate that we just cannot give a comprehensive treatment of all aspects of organic materials herein. 

A further feature of modern Raman spectroscopic microscopes is that the laser is polarized, allowing determination of, for example, depolarization ratios, and molecular orientation in crystals or liquid crystals. Care must be taken to account for the polarization response of the vertically ruled diffraction grating however. To date, there have been few or no polarization dependent studies of biological materials although recent studies have demonstrated that polarization dependent Raman can detect structural changes in the extracellular matrix associated with basal cell carcinoma. ... 

These materials also command premium prices and some require special processing. Examples are polyimides, polyetheretherketone, liquid-crystal polymers, polytetra-fluoroethylene, and polybenzimidazole (Odian GC (2004) Principles of polymerization. Wiley, New York Modern plastics encyclopedia, McGraw-Hill/Modern Plastics, New York). 

Presumed ferroelectric effects in liquid crystals were reported by Williams at RCA in Princeton, U. S. A., as early as 1963, and thus at the very beginning of the modern era of liquid crystal research [5]. By subjecting nematics to rather high dc fields, he provoked domain patterns that resembled those found in solid ferroelectrics. The ferroelectric interpretation seemed to be strengthened by subsequent observations of hysteresis loops by Kapustin and Vistin and by Williams and Heilmeier [7]. However, these patterns turned out to be related to electrohydrodynamic instabilities, which are well understood today (see, for instance, [8], Sec. 2.4.3 or [9], Sec. 2.4.2), and it is also well known that certain loops (similar to ferroelectric hysteresis) may be obtained from a nonlinear lossy material (see [10], Sec. 2.4.2). As we know today, nematics do not show ferroelectric or even polar properties. In order to find such properties we have to lower the symmetry until we come to the tilted smectics, and further lowering their symmetry by making them chiral. The prime example of such a liquid crystal phase is the smectic C. ... 

Modern refining technology uses tantalum and niobium fluoride compounds, and includes fluorination of raw material, separation and purification of tantalum and niobium by liquid-liquid extraction from such fluoride solutions. Preparation of additional products and by-products is also related to the treatment of fluoride solutions oxide production is based on the hydrolysis of tantalum and niobium fluorides into hydroxides production of potassium fluorotantalate (K - salt) requires the precipitation of fine crystals and finishing avoiding hydrolysis. Tantalum metal production is related to the chemistry of fluoride melts and is performed by sodium reduction of fluoride melts. Thus, the refining technology of tantalum and niobium involves work with tantalum and niobium fluoride compounds in solid, dissolved and molten states. 

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