Portal de Periódicos da CAPES

Characterization of director fluctuations in liquid crystals using the dipolar correlation effect of the stimulated echo

1996; Elsevier BV; Volume: 115; Linguagem: Inglês

10.1016/0927-7757(96)03601-1

1873-4359

Farida Grinberg, Rainer Kimmich, Elmar Fischer,

NMR spectroscopy and applications

Abstract The purpose of this work is to show that the stimulated-echo pulse sequence can be employed for the examination of slow collective motions in ordered systems. In nematics of low molecular weight (4′- n -pentyl-4-cyanobiphenyl) the attenuation of the ratio of the stimulated and primary echo amplitudes was measured as a function of the time delay between the first and the second 90° pulses. The attenuation of the echo quotient as well as the atypical (compared to the isotropic phase) oscillating behavior of the attenuation curves are described by means of stochastically time dependent interactions of dipolar coupled proton pairs. Slow director fluctuations are considered as a mechanism tending to average these interactions. Good agreement with the experimental data was obtained.