Mixing Effects on the Cotton-Mouton Constant of 3OCB and 5OCB in Isotropic Phase

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Abstract
To find a material with large magnetic-field-induced birefringence Δ n/H 2, we have studied the mixing effects on K C and (Δ n/H 2) T=T c of 4'-n-propyloxy-4-cyanobiphenyl (3OCB), which has the largest value of K C, and 4'-n-pentyloxy-4-cyanobiphenyl (5OCB), which has the largest value of (Δ n/H 2) T=T c among the cyanobiphenyls so far investigated. Here K C is the proportionality constant in the relation Δ n/H 2=K C/(T-T c *); (Δ n/H 2) T=T c is necessary because the relation may not hold as the temperature approaches the clearing point T c. The mixing is effective and both K C and (Δ n/H 2) T=T c attain the maxima at x=0.2 and 0.6, respectively, where x=[5 OCB]/([3 OCB]+[5 OCB]). The phase field in which the isotropic and nematic phases coexist appears to be less than 0.07°C. The K C(x) and T c(x) curves have mirror symmetry with respect to a line parallel to the abscissa; larger K C corresponds to lower T c. To understand their dependence on x, we have also discussed what phenomenological parameters in the Landau-de Gennes theory are responsible for K C and (Δ n/H 2) T=T c .