LINEAR VISCOELASTICITY OF SIDE-CHAIN LIQUID-CRYSTAL POLYMERS
LINEAR VISCOELASTICITY OF SIDE-CHAIN LIQUID-CRYSTAL POLYMERS
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DOI：
10.1080/02678299308026297
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发表时间：
1993-02-01
期刊：
影响因子：
2.2
通讯作者：
HALL, E
中科院分区：
文献类型：
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作者：
COLBY, RH;GILLMOR, JR;HALL, E
小振幅振荡剪切已被用于研究热致性液晶聚合物，具有介晶基团悬垂到柔性主链。所研究的聚合物形成了非晶和近晶玻璃，使粘弹性响应能够在很宽的频率范围内使用时间-温度叠加进行研究。与主链液晶聚合物相比，侧链聚合物在宽范围的应变振幅上表现出线性粘弹性响应，其独立于热历史和剪切历史。粘弹性响应对近晶-均质和近晶-各向同性转变非常敏感，但对向列相-各向同性转变不敏感，因为时间-温度叠加适用于该转变。我们通过计算聚合物扩散等于其线圈尺寸R的距离所需的时间τ（τ = R2/D）来比较粘弹性数据与扩散数据。在低于1/τ的频率下，侧链聚合物在其端部显示出粘弹性液体的终端响应特性。在近晶相，它们在低于1/τ的频率下仍然是强粘弹性的，并且在最低频率下接近粘弹性固体的终端响应。这种行为的影响进行了讨论。
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 tau that it takes a polymer to diffuse a distance equal to its coil size R (tau = R2/D). At frequencies lower than 1/tau, 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/tau, and approach the terminal response of a viscoelastic solid at the lowest frequencies. Implications of such behaviour are discussed.