Determination of Pitch in a Cholesteric DSCG-Water Lyomesophase by NMR Techniques

Nuclear Magnetic Resonance (NMR) techniques are used to determine the pitch in a cholesteric lyomesophase prepared by adding of l-alanine to a solution of disodiumcromoglycate (DSCG) in water. The method, which is particularly suitable for the study of bulk samples, consists of a combination of two independent types of measurements: (i) The effective reorientational correlation time of the director, due to molecular translational diffusion, is determined by a lineshape analysis of the deuterium resonances of the solvent D2O and/or deuterated l-alanine. (ii) The translational self-diffusion coefficients of both these constitutents is determined by a pulsed field-gradient spin-echo experiment. From the results of these measurements, the pitch and its dependence on the chiral dopant concentration is determined.