THE EFFECT OF MAGNETIC-FIELD AND CONVECTIVE FLOW ON NEMATIC DIRECTOR FLUCTUATIONS

The slow orientational fluctuations of the director in the nematic sta te of d-PAA have been studied by real-time neutron scattering. By anal ysis of the measured time series we have derived the Hurst exponent H as a function of the applied magnetic field and of the applied vertica l temperature difference of the sample. For zero values of both parame ters we found H greater than or equal to 0.9, indicating a high degree of temporal correlation between orientational fluctuations. At increa sing field or temperature gradient H approaches a value of 0.5, corres ponding to zero temporal correlations.