Applications lyotropic liquid crystalline state

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. 

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. 

Liquid crystalline polymers have been discussed in many texts and review papers [65, 400-413] during the last decade, in which the synthesis, processing, morphology, orientation and structure-property relations are described. The major applications of these materials have been as high modulus fibers and films, with unique properties due to the formation of ordered lyotropic solutions or thermotropic melts which transform easily into highly oriented, extended chain structures in the solid state. 

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