Dynamic Light Scattering Study of Nematic and Smectic-ALiquid Crystal Ordering in Silica Aerogel

The dynamical behavior of nematic and smectic- $A$ ordering of a liquid crystal in an aerogel host is studied by quasielastic light scattering. In the nematic phase, ordered domains are comparable to the pore size and generally frozen in orientation, with remnant orientation fluctuations having paranematic dynamics for a domain size distribution appropriate to the aerogel, and the coupling between domains giving rise to an additional slow glasslike relaxation. At lower temperatures a drastic slowing down, connected with a local nematic–to–smectic- $A$ transformation, is observed.