Thermotropic liquid crystals applications

Liquid crystals are mainly used for decorative purposes in cosmetics. Cholesteric liquid crystals are particularly suitable because of their iridescent color effects, and find applications in nail varnish, eye shadow, and lipsticks. The structure of these thermotropic liquid crystals changes as a result of body temperature, resulting in the desired color effect. In recent times, such thermotropic cholesteric liquid crystals have been included in body care cosmetics, where they are dispersed in a hydrogel. Depending whether this dispersion requires stirring or a special spraying process, the iridescent liquid crystalline particles are distributed statistically in the gel (Estee Lau-... 

On the other hand, the interest towards this field is accounted for by the possibility to create polymeric systems, combining the unique properties of low-molecular liquid crystals and high molecular compounds, making it feasible to produce films, fibers and coatings with extraordinary features. It is well-known that the utilization of low-molecular thermotropic liquid crystals requirs special hermetic protective shells (electrooptical cells, microcapsules etc.), which maintain their shape and protect LC compounds from external influences. In the case of thermotropic LC polymers there is no need for such sandwich-like constructions, because the properties of low-molecular liquid crystals and of polymeric body are combined in a single individual material. This reveals essentially new perspectives for their application. 

Applicability of Work on Hydrodynamic Instabilities of Thermotropic Liquid Crystals... 

Since the description of liquid crystallinity for cholesteryl benzoate and cholesteryl acetate at the end of the 19th century by Reinitzer [1], an intense activity has been devoted to thermotropic liquid crystals, especially since the early 1970s, owing to the fabrication and application of liquid crystal displays in electronic technology. 

The subject of liquid crystals has now grown to become an exciting interdisciplinary field of research with important practical applications. This book presents a systematic and self-contained treatment of the physics of the different types of thermotropic liquid crystals - the three classical types, nematic, cholesteric and smectic, composed of rod-shaped molecules, and the newly discovered discotic type composed of disc-shaped molecules. The coverage includes a description of the structures of these four main types and their polymorphic modifications, their thermodynamical, optical and mechanical properties and their behaviour under external fields. The basic principles underlying the major applications of liquid crystals in display technology (for example, the twisted and supertwisted nematic devices, the surface stabilized ferroelectric device, etc.) and in thermography are also discussed. 

Chung TS, editor. Thermotropic liquid crystal polymers thin-film polymerization, characterization, blends, and applications. Lancaster, PA TechnomicPub. Co. 2001. ISBN 1566769434. 

Thermotropic liquid crystals have many applications in science, technology, and medicine. The familiar black-and-white displays in timepieces and calculators are based on the properties of these substances. Transparent aligning agents made of tin oxide (Sn02) applied to the lower and upper inside surfaces of the fiquid crystal cell preferentially orient tfie molecules in the nematic phase by 90° relative to each other. In this way, the molecules become twisted through the fiquid crystal phase. When properly adjusted, this twist rotates the plane of... 

Thermotropic Liquid Crystal Polymers Thiil-film Polymerizadon, Characterization. Blends, and Applications... 

A. A. Collyer, Thermotropic liquid crystal polymers for engineering applications. Materials Science and Technology, 5, 309 (1989). 

It was realized in the early 1970s that the unusual properties of thermotropic liquid crystals held great promise for use in flat-panel electronic displays and other optical control applications. The advantages particular to Uquid crystals of a very large (if not especially fast) electrooptic effect induced by CMOS-compatible voltages and of microwatts per square centimeter power consumption were identified at an early stage. With the discovery of chemically stable nematic liquid crystals, such as the... 

From a historical point of view as well as due to their applications, thermotropic and lyotropic liquid crystals have always been treated separately. While thermotropics and the concept of liquid crystallinity in general were discovered as late as in 1888 [3], lyotropic phases were known to mankind since the Bronze Age [4], as they occur during the soap-making process. Due to this, lyotropic liquid crystals find their main applications in the detergent industry and in cosmetics. As various biological systems, e.g. cell membranes, take a lyotropic liquid crystalline form, they also possess some medical and pharmaceutical importance [5]. In contrast, thermotropic liquid crystals are used for completely different applications, e.g. for displays, thermography, tunable filters or lasers [6]. Thus, it is not astonishing, that two distinct fields of research evolved for the two types of liquid crystals. However, thermotropic and lyotropic liquid crystals share a common state of matter with many similarities. For example, many mesophases which occur in thermotropics can also be found in lyotropics. Still, there are some thermotropic phases which do not seem to have a lyotropic counterpart. 

In the present applications we have used only thermotropic liquid crystals of the nematic and cholesteric type. 

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