DYNAMICS OF A LIQUID-CRYSTAL BY DEUTERIUM NMR - THE ANALYSIS OF DIRECTOR FLUCTUATIONS AND REORIENTATION OF MOLECULES

The zero-frequency spectral densities J(0)(0) data(1) for the liquid c rystal p-(methoxybenzylidine)-p-n-butylaniline (MBBA) is quantitativel y interpreted using a model that includes director fluctuations and ro tational diffusion of symmetric rotors in a nematic phase. The contrib ution to J(0)(0) from director fluctuations has mainly a second-order component, whereas the first-order contribution to J(1)(omega) is supp ressed in the megahertz region (Larmor frequencies are 15.3 and 46 MHz ) due to the high-frequency cutoff, which is estimated to be around 3- 10 MHz for MBBA. A global target approach is used in the analysis of a ll the available spectral densities. As a result, motional parameters and a molecular prefactor for director fluctuations are obtained in th e nematic phase of MBBA.