Dendrimeric Liquid Crystals:  Isotropic−Nematic Pretransitional Behavior

Kerr measurements, ellipsometry, and quasielastic light scattering have been used to probe nematic fluctuations and nematic wetting at an isotropic liquid crystal−substrate interface in four generations of liquid crystalline monodendrons and dendrimers. We find that the pretransitional behavior is q...

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Bibliographic Details
Published in:Macromolecules 1996-11, Vol.29 (24), p.7813-7819
Main Authors: Li, Jian-feng, Crandall, Karl A., Chu, Peihwei, Percec, Virgil, Petschek, Rolfe G., Rosenblatt, Charles
Format: Article
Language:English
Subjects:
Applied sciences
Exact sciences and technology
Organic polymers
Physicochemistry of polymers
Properties and characterization
Thermal and thermodynamic properties
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Summary:Kerr measurements, ellipsometry, and quasielastic light scattering have been used to probe nematic fluctuations and nematic wetting at an isotropic liquid crystal−substrate interface in four generations of liquid crystalline monodendrons and dendrimers. We find that the pretransitional behavior is qualitatively similar to that of low molecular weight liquid crystals, exhibiting a Landau-like divergence of the relaxation time and a logarithmic divergence of the optical retardation on approaching the nematic−isotropic phase transition from above. Quantitatively, we find that the transition temperatures of the monodendrons are 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 ≤ 1.0.
ISSN:0024-9297
1520-5835
DOI:10.1021/ma961116b