Odd-Even Effect on Nematic-SmAd Phase Boundary and SmAd-Structure in Homologous Binary Systems of Cyanobiphenyl Mesogens: 4-Alkyl-4'-cyanobiphenyl (nCB) and 4-Alkoxy-4'-cyanobiphenyl (nOCB)


Phase behaviors of two homologous binary systems of 4-alkyl-4'-cyanobiphenyl (nCB, n being the number of carbon atoms in the alkyl-chain) and 4-alkoxy-4'-cyanobiphenyl (nOCB) were investigated. Their phase diagrams were drawn against an averaged chain length, n*. The phase boundary curves between neamtic (N) and smectic Ad (SmAd) phases in nCB/mCB (n = 3 - 6; m = 8, 9) binary systems were classified into four depending on four combinations of even- and odd-numbered n and m; even/even, odd/even, even/odd, and odd/odd. The similar odd-even effect was confirmed for nOCB/mOCB (n = 5, 6; m = 8, 9) binary systems. To elucidate the odd-even effect on the phase diagrams, the SmAd-structures were investigated through an analysis of n (n*)-dependence of the layer spacing of the SmAd-structure, dSmAd, of neat nCB (n = 8 - 10), neat nOCB (n = 8-10) and nCB/8CB (n = 0-7) binary mixtures. The odd-even effect, the behavior of 0CB/8CB system and the difference between nCB and nOCB were clarified based on their SmAd-structures.
(J. Phys. Chem. B, 121, 1438-1447 (2017))

Reentrant Nematic Phase in 4-Alkyl-4'-cyanobiphenyl (nCB) Binary Mixtures

Shuhei FUJUMIRA, Yasuhisa YAMAMURA, Mafumi HISHIDA, Shigenori NAGATOMO and Kazuya SAITO

Appearance of reentrant nematic phase was identified in nCB/8CB (n = 1- 6) binary mixtures using differential scanning calorimetry, small angle X-ray diffraction, and polarizing microscopy with photomonitor. Phase diagrams can roughly be unified if plotted against the average number of alkyl chain length. Distinction was recognized for the phase boundaries between nematic and smectic A phases of even and odd n of the minor component nCB. The character of 8CB as "SmA former" is briefly discussed.
(Liq. Cryst., 41, 927 (2014))

See also Reentrace Mechanism in Thermotropic Cubic LC.

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