Shear and time‐dependent rheology of a fully nematic thermotropic liquid crystalline copolymer
Shear and time‐dependent rheology of a fully nematic thermotropic liquid crystalline copolymer
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全向列热致液晶共聚物的剪切和时间依赖性流变学
DOI：
10.1122/1.550116
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发表时间：
1990
影响因子：
3.3
通讯作者：
M. Denn
中科院分区：
文献类型：
--
作者：
D. S. Kalika;D. Giles;M. Denn
报道了由80%对羟基苯甲酸/20%聚对苯二甲酸乙二醇酯组成的完全双折射热致液晶聚合物的流变学测量。该聚合物显示剪切稀化行为，在80倍剪切速率下具有恒定的幂律指数;未观察到剪切独立平台（区域II）。动态时间扫描表明高灵敏度的流变参数的热历史，显然是由于结晶退火。这些退火效应可以通过适当的热循环消除。由于边缘断裂的发生，在高剪切速率下的扭转测量（锥体和平板）受到限制。这种不稳定性通常伴随着由同心环组成的不寻常的样品纹理，当聚合物熔体中发生脱气时，这种纹理特别明显。
Rheological measurements are reported for a fully nematic thermotropic liquid crystalline copolyester composed of 80% p‐hydroxybenzoic acid/20% poly(ethylene terephthalate). The polymer displays shear thinning behavior with a constant power‐law index over eight decades of shear rate; no shear‐independent plateau (region II) is observed. Dynamic time sweeps indicate a high sensitivity of the rheological parameters to thermal history, apparently resulting from crystalline annealing. These annealing effects could be erased by appropriate thermal cycling. Torsional measurements (cone‐and‐plate) were limited at high shear rates by the occurrence of edge fracture. This instability was typically accompanied by an unusual sample texture composed of concentric rings, which was particularly distinct when offgassing had occurred in the polymer melt.