The structures and conformations of mesogenic molecules in the pre-transitional region of the isotropic phase: 5OCB and MBBA and their mixtures

Abstract

A nuclear magnetic resonance spectrometer operating with a magnetic field of 23.49 T, corresponding to 1000 MHz for protons, has been used to study mesogenic molecules N-(4-methoxybenzylidene)-4-butylaniline (MBBA) and 4-pentyloxy-4′-cyanobiphenyl (5OCB) and their approximately equimolar mixture at temperatures above the isotropic to nematic phase transition. In this strong magnetic field, B 0, the molecules acquire a strong partial alignment whose magnitude depends on , and also on the anisotropic intermolecular interactions, which grow in strength as the isotropic to nematic phase transition is approached. The well-resolved spectra obtained are analysed to obtain magnetic field induced dipolar couplings between proton (1H), and between 1H and carbon nuclei, which are used to investigate the structure, conformational distribution and orientational order in both the pure compounds and in their mixtures.