INTERACTIONS OF ALUMINUM IONS IN CATIONIC AND ANIONIC AMPHIPHILIC NEMATIC LIQUID-CRYSTALLINE SOLUTIONS

1H, 2H, and 27Al nuclear magnetic resonance spectroscopies have been used to study some of the phenomenological aspects of the interactions of Al(H2O)63+ and Al(OH)4- in both cationic and anionic lyotropic liquid crystalline solutions. It was found for the cationic mesophase prepared from tetradecyltrimethylammonium bromide that the 27Al quadrupole splitting from Al(H2O)63+ was constant at 60 Hz throughout the pH range 1.7-3.6. In the same mesophase system the quadrupole splitting from Al(OH)4- was constant at about 35 Hz throughout the pH range 8.8-11.7. The quadruple splitting from Al(H2O)63+ increased almost 4-fold when tetradecyltrimethylammonium bromide was replaced by decylammonium bromide. In the anionic mesophase prepared from sodium decyl sulfate, the 27Al quadrupole splitting from Al(H2O)63+ was about 450 Hz throughout the range of pH from 1.5 to 3.6. At higher pH of about 10.5 the quadrupole splitting from the Al(OH)4- ion was approximately 500 Hz for the decyl sulfate system and about 830 Hz from a potassium dodecanoate mesophase. Ion competition interactions of Al(H2O)63+ between sulfate and amphiphile were carried out both in cationic and anionic mesophases. In the tetradecyltrimethylammonium system a substantial upward curvature in the quadrupole splitting with increase in Al(H2O)63+/SO42- ion-paired product was observed. In contrast to this, a significant decrease in quadrupole splitting with proportion of ion-paired product was observed in the anionic decyl sulfate system. These results are consistent with a model that allows Al(H2O)63+ to approach a positively charged micellar surface when in solution as an ion-paired product. The product will then be more easily aligned by the anisotropic forces of the micelle, and this will lead to an increase of the quadrupole splitting. A similar ion-paired product in the anionic system will tend to remove the Al(H2O)63+ moiety from the micellar surface, thus leading to a decrease in the observed splitting. © 1990 American Chemical Society.