DYNAMIC LIGHT-SCATTERING FROM NEMATIC MONODOMAINS CONTAINING MESOGENIC POLYMERS OF DIFFERING ARCHITECTURES

Dynamic light scattering studies of nematic monodomains which contain side-chain and main-chain liquid crystal polymers dissolved in a low molar mass nematogen, 4'-n-pentyl-4-cyanobiphenyl (5CB), are described. The relaxation rates of the splay, twist, and bend director distortions have been measured and compared with those of pure 5CB at comparable temperature decrements T(N-I)-T from the nematic to isotropic transition. Addition of both side-chain and main-chain polymers results in substantial decreases in the relaxation rates of all three modes. However, for the side-chain polymers, the relative decrease in the relaxation rate of the bend mode is comparable to or larger than those of the twist and splay modes and is strongly dependent on backbone flexibility and spacer length. In contrast, for main-chain polymers, the relative decrease in relaxation rates is large for splay and twist and small for the bend mode. This dynamical behavior is consistent with the expectation that the chain backbone orients perpendicular to the director for side-chain polymers and extends parallel to the director for main-chain polymers.