The Effect of Molecular Structure on the Formation of Induced Nematic Phases in Binary Mixtures

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Abstract
A variety of 4-halophenyl-4′-alkoxybenzoates and 4-alkoxyphenyl-4′-halobenzoates were synthesized, their mesomorphic properties determined and compared with those of the analogous halo anils. The ability of these esters to form induced nematic phases (INPs) in binary mixtures was studied along with a variety of other mesogenic type compounds not having a nematic phase. The contact method was used to screen 258 mixtures for INPs in an attempt to determine which molecular structural features favored formation of this phase in binary mixtures. INPs were observed in many of these mixtures and with a wide variety of structures. Phase diagrams of some of these mixtures were obtained in order to compare the abilities of certain structural features to form INPs. Two types of diagrams were observed. Type I showed a narrow INP range ocurring over most of the composition range between two nearly linear SN and MI curves and was observed only when the two components had similar molecular lengths either short or long. In Type II, wide range INPs were observed between a nearly linear MI curve and a non-linear SN curve with their maximum range in the region of the minimum and was observed only when the two components had a large difference between their molecular lengths. The range of these INPs was largest at compositions of <50% of the longest molecule. Phase diagrams also indicated that the INP was less favored as either the alkyl chain length or the halogen size increased. The steric effect of an α-methyl group on the acid alkyl chain in the 4-alkoxyphenyl-4′-alkylbenzoates on nematic properties reported earlier was also observed with INPs in these mixtures.

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