DENDRIMERIC LIQUID-CRYSTALS - ISOTROPIC-NEMATIC PRETRANSITIONAL BEHAVIOR

Kerr measurements, ellipsometry, and quasielastic light scattering hav e been used to probe nematic fluctuations and nematic wetting at an is otropic liquid crystal-substrate interface in four generations of liqu id crystalline monodendrons and dendrimers. We find that the pretransi tional behavior is qualitatively similar to that of low molecular weig ht liquid crystals, exhibiting a Landau-like divergence of the relaxat ion time and a logarithmic divergence of the optical retardation on ap proaching the nematic-isotropic phase transition from above. Quantitat ively, we find that the transition temperatures of the monodendrons ar e typically about 0.5 K above the supercooling limit of the isotropic phase and that the orientational viscosities may be fit to a power law in molecular weight M(n), where the exponent less than or equal to 1. 0.