Linear viscoelasticity of side chain liquid crystal polymer
作者:
R.H. Colby,
J.R. Gillmor,
G. Galli,
M. Laus,
C.K. Ober,
E. Hall,
期刊:
Liquid Crystals
(Taylor Available online 1993)
卷期:
Volume 13,
issue 2
页码: 233-245
ISSN:0267-8292
年代: 1993
DOI:10.1080/02678299308026297
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
Small amplitude oscillatory shear has been used to study thermotropic liquid-crystalline polymers that have mesogenic groups pendant to flexible backbones. The polymers studied form nematic and smectic glasses, enabling viscoelastic response to be studied over a wide range of frequencies using time-temperature superposition. In contrast to main chain liquid-crystalline polymers, the nematic side chain polymers exhibit linear viscoelastic response over a wide range of strain amplitudes that is independent of thermal and shear histories. Viscoelastic response is very sensitive to smectic-nematic and smectic-isotropic transitions, but insensitive to the nematic-isotropic transition, as time-temperature superposition applies across this transition. We compare viscoelastic data with diffusion data by calculating the time τ that it takes a polymer to diffuse a distance equal to its coil sizeR(τ=R2/D). At frequencies lower than 1/τ side chain polymers in their nematic show the terminal response characteristic of viscoelastic liquids. In their smectic, they are still strongly viscoelastic at frequencies lower than 1/τ and approach the terminal response of a viscoelastic solid at the lowest frequencies. Implications of such behaviour are discussed.
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