PHASE-BEHAVIOR AND ORDERING CHARACTERISTICS OF SOME CHAIN MOLECULES DISSOLVED IN A NEMATIC LIQUID-CRYSTAL, 4'-METHOXYBENZYLIDENE-4-N-BUTYLANILINE

Phase diagrams were reported for binary mixtures comprising a series of dimethyl ethyleneglycol ethers CH3O(CH2CH2O)xCH3 (x=1-3) (DMEG) and a nematogenic solvent 4'-methoxybenzylidene-4-n-butylaniline (MBBA) at low solute mole fraction. For a comparison purpose, measurements were also carried out for n-hexane hosted in the same solvent. Following Martire et al., the slopes, beta(N) and beta(I), of the nematic and isotropic phase boundary lines have been used as a measure of the compatibility of nonmesomorphic solutes with the nematic phase. The beta values of the DMEG series were found to increase rapidly with the chain length in contrast to those reported for n-alkanes CH3(CH2)n-2CH3. The H-2 NMR technique was extensively employed to elucidate the orientational order of the individual components in the mixture. In accordance with the trend observed in the phase behavior, the DMEG series exhibit a greater reduction of nematic order when compared at the same solute concentration of hydrocarbon analogs. The deuterium quadrupolar splitting DELTAnu were observed for the methylene and methyl deuterons of the solute molecule. The ratio of quadrupolar splittings DELTAnu/DELTAnu(j) which represents the relative orientation of the CD bonds at sites i and j, were found to remain nearly invariant over a wide range of concentration and temperature. It has been concluded from the RIS analysis that the flexible chain molecules examined prefer to take somewhat more elongated forms to facilitate alignment in the nematic field as compared with those in the conventional isotropic solution.