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 ( n CB, n being the number of carbon atoms in the alkyl chain) and 4-alkoxy-4′-cyanobiphenyl ( n OCB) were investigated. Their phase diagrams were drawn against an averaged chain length, n *. The phase boundary curves between neamtic (N) and smectic A d (SmA d ) phases in n CB/ m CB ( 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 n OCB/ m OCB ( n = 5, 6; m = 8, 9) binary systems. To elucidate the odd–even effect on the phase diagrams, the SmA d structures were investigated through an analysis of n ( n *) dependence of the layer spacing of the SmA d structure, d SmAd, of neat n CB ( n = 8–10), neat n OCB ( n = 8–10), and n CB/8CB ( n = 0–7) binary mixtures. The odd–even effect, the behavior of 0CB/8CB system, and the difference between n CB and n OCB were clarified based on their SmA d structures.