ENANTIOTROPIC NEMATIC PHASES OF QUATERNARY AMMONIUM HALIDE SALTS BASED ON TRIOCTADECYLAMINE

The neat phases of a series of quaternary ammonium halides based on tr ioctadecylamine have been investigated by optical microscopy, differen tial scanning calorimetry, and H-2 NMR spectroscopy. Phase behaviour d epends primarily on the structure of the fourth substituent on nitroge n and the thermal history of the samples. For instance, the iodide sal ts with methyl, ethyl, or propyl as the fourth substituent form enanti otropic nematic phases, while those with a proton or a longer alkyl su bstituent exhibit complex phase behaviour that does not include a liqu id crystalline phase. Possible reasons are advanced for the unpreceden ted formation of nematic phases.