Locally anisotropic motion in a macroscopically isotropic system: displacement correlations measured using double pulsed gradient spin-echo NMR

We propose a novel application of double pulsed gradient spin-echo NMR in which two pairs of gradient pulses are used successively to encode the spin magnetization. These pairs were applied with gradient directions collinear and orthogonal, and the results were compared. The method can be used to detect local diffusion anisotropy even when the distribution of domain directors in the sample is isotropic. The degree of the difference between collinear and orthogonal echo attenuation responses indicates the nature of that local anisotropy. We applied this method to a polydomain lyotropic liquid crystal system, Aerosol OT-water, and detected the local diffusion anisotropy directly. Copyright (C) 2002 John Wiley Sons, Ltd.