Abstract
The dynamic moduli of side-group liquid-crystalline polymers (SG-LCPs) having methacry- late backbone, hexamethylene spacer, and phenyl benzoate mesogens are characterized as a function of molecular weight in the isotropic, nematic, and smectic phases. Molar mass was varied from 3 x lo6 to 3 x lo6 g/mol, corresponding to the range where the onset of entanglement is observed in the isotropic phase (approximately l-lOMe,,so). Nematic order produces a profound change in the dynamics of the entangled SG-LPCs relative to the isotropic phase; however, this effect is absent in the unentangled SG-LCPs. Oscillatory shear with large amplitude (yo z 40%) is effective in inducing macroscopic alignment in the nematic phase for all the SG-LCPs studied. Smectic order increases the elastic character of the fluid, but its incremental effect in a system that is entangled is relatively small. Large-amplitude shearing can be used to alter the microstructure in the smectic liquid: shearing the smectic phase produces a decrease in modulus, whereas shearing in the nematic phase followed by cooling into the smectic phase produces an increase in modulus.
Published Version
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