EVIDENCE OF DYNAMIC LONG-RANGE CORRELATIONS IN A NEMATIC-LIQUID-CRYSTAL-AEROGEL SYSTEM

Dynamical behavior of a nematic liquid crystal in a silica aerogel hos t near the nematic-isotropic phase transition was studied by quasielas tic light scattering. Just below the nematic-isotropic phase transitio n temperature two modes were observed. The faster mode does not depend on the scattering vector and is attributed to the intrapore orientati onal fluctuations. Close to the transition, its inverse relaxation tim e steeply increases due to the pretransitional order parameter fluctua tions in smaller pores, where the phase transition to the isotropic ph ase occurs at lower temperatures. The second, slower mode has a quadra tic dependence on the scattering vector, giving evidence of correlated interpore fluctuations. Their relaxation rate is slower than that of the bulk orientational fluctuations and approaches zero at the transit ion. This is not observed in the bulk.