Rheology and flow-induced liquid crystal phase transitions in thermotropic polyethers
Rheology and flow-induced liquid crystal phase transitions in thermotropic polyethers
复制标题
热致聚醚的流变学和流动诱导液晶相变
DOI：
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发表时间：
1994
影响因子：
4.5
通讯作者：
V. Percec
中科院分区：
文献类型：
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作者：
D. Heberer;J. Odell;V. Percec
本文研究了热致性液晶聚醚的相行为、粘度、温度、分子量和剪切速率之间的相互关系。定量比较各向同性相和双相的粘度;发现粘度相对于温度的正变化，其中各向同性粘度比液晶粘度高约一个数量级。在液晶和各向同性相的粘度依赖于分子量定义明确的馏分进行了研究。在液晶状态下，粘度与M3.5-5成比例。温度变化引起的粘度变化对各向同性相的影响大于对液晶相的影响。没有证据表明负的第一法向应力差。最后，它示出了如何可以通过剪切各向同性相的材料来改变材料的相图。这通过在略高于Ti的温度下剪切稀化区域的开始是明显的，这可以归因于剪切诱导的液晶性的形成。
This work investigates the interdependence of the phase behaviour, viscosity, temperature, molecular weight and shear rates of thermotropic liquid crystalline polyethers. The viscosity of the isotropic and nematic phases are quantitatively compared; a positive variation in viscosity with respect to temperature is found, with the isotropic viscosity being about an order of magnitude higher than the liquid crystalline viscosity. The dependence of viscosity upon molecular weight of well defined fractions is investigated in both the liquid-crystal and isotropic phases. In the liquid crystalline state the viscosity scales with M3.5–5. Variations in the viscosity due to temperature changes affect the isotropic phase more than the liquid crystal phase. No evidence for a negative first normal stress difference is seen. Finally, it is shown how the phase diagram of the material can be altered by shearing the material in the isotropic phase. This is evident by the onset of a shear thinning region at temperatures slightly above Ti, which can be attributed to the formation of shear induced liquid crystallinity.