SQUID STUDIES OF ALPHA,OMEGA-BIS[(4,4'-CYANOBIPHENYL)OXY]ALKANES AND ELUCIDATION OF THE ORIENTATIONAL ORDER PARAMETER

The magnetic susceptibilities of dimer liquid crystals such as NCPh2O (CH2)nOPh2CN (n = 9, 10) have been measured by a SQUID magnetometer. The anisotropies of the susceptibility, Δχ = χ1- χ1, were found to increase abruptly at the isotropic to nematic transition (TNI), followed by a gradual increase over the entire range of the nematic phase. At the onset of crystallization, a sharp decrease of the Δχ value was observed. The Δχ values in the very vicinity of TNI were estimated by extrapolation from those obtained at stable nematic temperatures according to the empirical Haller equation: 0.889 and 1.062 × 10-9 m3 kg-1, respectively, for n = 9 and 10 at n = TNI - 0.5 K. These results have been interpreted within the framework of the rotational isomeric state approximation, the effect arising from the conformational anisotropy of the flexible spacer being strictly taken into account. The order parameters of the mesogenic core axis thus estimated were found to be consistent with those directly observed at just below TNI by the2H NMR technique using mesogen-deuterated samples. © 1990, American Chemical Society. All rights reserved.