Reversal of the Sign of the Diamagnetic Anisotropy of Lyotropic Nematic mesophases Induced by an Aromatic Solute

Abstract

Abstract In four lyotropic nematic mesophase systems the sign of the anisotropy of the diamagnetic susceptibility was observed to change with the addition of sufficient amounts of benzenesulfonate. Four series of mesophases were examined, two with initially postive diamagnetic anistopies and two with initially negative anisotropies prepared using alkyltrimethylammonium, decylammonium and dodecanoate surfactancts. The sign of the diamagnetic anisotropy and the order parameters of the benzenesulfonate ion were determined from the proton NMR spectra. The concentraion of benzene-sulfonate ion necessary to form a mesophase with zero diamagnetic anisotropy can be explained in terms of the relative contributions to the macroscopic diamagnetic susceptibility of the aromatic rings and the hydrocarbon chains.