Location and Average Alignment of Alkylpyridinium Ions in Cationic Nematic Lyomesophases

Abstract

Deuterium quadrupole splittings from the aromatic ring of series of deuterium labeled n-alkylpyridinium ions with linear n-alkyl groups from C 1 to C 16 have been measured using 2 H-NMR spectroscopy. These splittings were used to calculate the two order parameters describing the average alignment of the individual pyridinium rings, and these values were used to determine the location and preferred orientation of the ions when contained in either of the lyotropic liquid crystals of this study. Two cationic mesophases, prepared from either hexadecylpyridinium chloride or tetradecyltrimethylammonium bromide, were used as the host systems. The smaller alkylpyridinium ions(C 1 -C 5 ) were found predominantely in the interstitial water. The intermediate size ions (C 6 -C 10 ), which were distributed more effectively into the micelle, have a disruptive effect in the mesophase, probably a result of modifications in the degree of alignment of the micelle, possibly because of modifications of its internal dynamics. Differences in the symmetry properties of the positively charged headgroups were found to impose restrictions on the motion of the dissolved alkylpyridinium ions.