The Alignment of Lyotropic Liquid Crystals Formed by Hexadecyltrimethylammonium Bromide in D2O in a Magnetic Field

The alignment of lyotropic liquid crystals formed by hexadecyltrimethylammonium bromide (CTAB, where C stands for cetyl) with D 2 O was studied by the use of 2 H NMR. At CTAB/D 2 O concentrations between 1.01 and 1.29 mol/kg, liquid crystal domains aligned in the magnetic field within a few hours. The dependence of the characteristic alignment time on concentration and temperature has been determined. At higher concentrations, no alignment took place due to the high viscosity of the system. At lower concentrations, the alignment could not be observed by 2 H NMR. The addition of sodium salicylate (NaSal), at equal molar concentrations of CTAB and NaSal, changed the orientation of the micelles from parallel to the magnetic field to perpendicular to the field. Line-shape simulations were carried out to give estimates on the rate of exchange between free D 2 O molecules and those bounded to the micelles, as well as on the deuterium quadrupole splittings for D 2 O molecules bound to micelles. The dependence of the characteristic alignment time on the strength of magnetic field was also studied.