The structures and conformations of mesogenic molecules in the pre-transitional region of the isotropic phase: 5OCB and MBBA and their mixtures
Résumé
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 B-0(2), 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 (H-1), and between H-1 and carbon nuclei, which are used to investigate the structure, conformational distribution and orientational order in both the pure compounds and in their mixtures.