Abstract
Liquid crystals, compounds and mixtures with positive dielectric anisotropies are reviewed. The mesogenic properties and physical chemical properties (viscosity, birefringence, refractive indices, dielectric anisotropy and elastic constants) of compounds being cyano, fluoro, isothiocyanato derivatives of biphenyl, terphenyl, quaterphenyl, tolane, phenyl tolane, phenyl ethynyl tolane, and biphenyl tolane are compared. The question of how to obtain liquid crystal with a broad range of nematic phases is discussed in detail. Influence of lateral substituent of different kinds of mesogenic and physicochemical properties is presented (demonstrated). Examples of mixtures with birefringence ∆n in the range of 0.2–0.5 are given.
Highlights
Compounds 86d–90d, Table 12, with naphthalene moiety have a nematic phase only, but their clearing points are lower than observed for phenyltolane families, especially when the naphthalene unit is placed on the left side of molecules
More interesting than quaterphenyls, are their four-ring analogues with the triple bond positioned inside the core, see compounds 113–118, see Table 15
High birefringence liquid crystal mixtures are necessary for application in visible, infrared, GHz and THz ranges of electromagnetic radiation
Summary
New types of liquid crystal displays and devices are considered, wherein response times may be less than 1 ms For this purpose, ―blue phase‖ mode [12,13,14] or other cholesteric modes [15]. The main area of application for very high birefringence LC is in infrared spectral range [16,17,18] and recently, the interest is gained to GHz and THz ranges They are connected with telecommunication devices needs or nondestructive microwaves apparatus to control goods and people [19], cholesteric lasers [20,21], manufacturing tunable metamaterial [22,23,24,25]. To reanalyze the experimental results that have been obtained so far may be helpful for this task
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