Nematic-isotropic pretransitional behaviour in dimers with odd and even spacer lengths

Abstract

Abstract Magnetic field induced optical birefringence measurements in the isotropic phase are reported for two members of a series of phenyl benzoate dimers: one having an odd number of methylene units in the spacer and one having an even number. The discontinuity at the nematic-isotropic transition, as determined by the difference between the first order phase transition temperature TNI and the supercooling limit of the isotropic phase T∗, is approximately 8 ± 3 times larger for the even species than for the odd. In addition, the product of the Cotton-Mouton coefficient dΔn/dH2 and T–T∗ is the same for both materials. In terms of both steric and molecular field theories, the results indicate that the orientations of the terminal mesogenic groups are essentially uncorrected in the isotropic phase.