SOLUTE INDUCED LIQUID-CRYSTALLINE BEHAVIOR OF A QUATERNARY AMMONIUM SALT AND ITS APPLICATION TO STRUCTURE DETERMINATION

A new liquid crystalline phase, induced by the addition of small amoun ts of a non-mesogenic solute (such as dimethyl sulphoxide or methyl io dide) to a quaternary ammonium salt, N-methyl-N,N,N-trioctadecylammoni um iodide (MTAI), has been detected by NMR and optical microscopic stu dies. In some cases, there is a coexistence of nematic and smectic pha ses. Information on the ordering of the phases in the magnetic field o f the spectrometer has been derived from NMR spectra of a dissolved mo lecule, C-13-enriched methyl iodide. The low order parameter of the pu re thermotropic nematic phase of the salt provides first-order spectra of the dissolved oriented molecules. Analyses of spectra of cis,cis-m ucononitrile exemplifies the utility of the MTAI nematic phase in the determination of structural parameters of the solute.