Evidence of dynamic long-range correlations in a nematic-liquid-crystal-aerogel system

Dynamical behavior of a nematic liquid crystal in a silica aerogel host near the nematic-isotropic phase transition was studied by quasielastic light scattering. Just below the nematic-isotropic phase transition temperature two modes were observed. The faster mode does not depend on the scattering vector and is attributed to the intrapore orientational fluctuations. Close to the transition, its inverse relaxation time steeply increases due to the pretransitional order parameter fluctuations in smaller pores, where the phase transition to the isotropic phase occurs at lower temperatures. The second, slower mode has a quadratic 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 transition. This is not observed in the bulk.