Nematic range

The first report on the liquid crystalline properties of these compounds was published by Gray and Mosley [44] in 1976. The series of 4 -n-alkyl-4-cyanobiphenyls (CBn) have been widely studied by different methods due to their readily accessible nematic ranges around room temperature. The compounds have the phase sequences crystal-nematic-isotropic for CBS, CBIO, and monotropic nematic for CBS, CB4 crystal-smectic A-nematic-isotropic for CB9 crystal-smectic A-isotropic for CBll. The lower homologous CB2 is nonmesogenic. The general chemical structure of the compounds CBn is presented in Fig. 1. 

The complexes show SmA mesophases, except the 2-fluorohexyloxy derivative, which shows a narrow nematic range and the 2-fluoroiodo derivative, which is not a liquid crystal. The transition temperatures of the chloro complexes compared with... 

X Y Smectic range (°C) Nematic range (°C) Calcd. Anal. (%) Found ... 

Bayle presented liquid crystal 34 (Scheme 19) bearing four aromatic units linked by ester and azo functional groups [56]. Two butyloxy groups are attached at the ends of the molecule and the crown ether is bound at the side of the molecule. The nematic phase exhibited by 34 is quite broad (AT = 96 K). Upon complexation with LiBF4, the nematic range diminishes with increasing amounts of added salt and disappears completely at 0.5 equiv. of added LiBF4 which is most likely due to the formation of a 2 1 crown lithium complex. From 0.2 equiv. of salt, a smectic... 

Analytical Properties Separation of substituted phenols selectivity is best at the lower end of the nematic range... 

Ferrocene derivatives 15 exhibited remarkable liquid crystal properties (Fig. 9-13). Indeed, they all gave rise to enantiotropic mesophases. Structures with n = 1 to 11 showed nematic phases. From n = 12 a smectic C phase formed. The latter was monotropic only for 15 (n = 12). The smectic C domain increased from n = 13 to n = 16, and, inversely, the nematic range narrowed. The last member of this series (n = 18) presented one smectic C phase between 159 °C and 179 °C. A nematic to smectic C transition and a focal-conic texture of a smectic C phase are presented in Figs. 9-14 and 9-15, respectively. 

Nearly exact numerical solutions of the Smoluchowski equation show that for the Maier-Saupe potential, A < 1 when S = S2 > 0.524. For the Onsager potential, A < 1 for all values of the order parameter within the nematic range. Values of A for the Onsager potential are plotted in Fig. 11-18. 

Contact preparations of complexes 106b and 111 with alkanes revealed the induction of a nematic phase with the complete destabilization of the thermotropic smectic phases. For both complexes, mixing with solvents resulted in the substantial depression of both melting and clearing temperatures. In the case of 106b, the nematic range... 

Nematic LC have good lubricating properties which seem to be best in the nematic range. Thus a LC mixture with a large nematic range has to be preferred. 

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