Dependence of flow behavior of complex fluids in elongational flows and change in structure on elongational property of fluids

我们考虑了复杂流体的拉伸性质起重要作用的流动。本文从众多复杂流体中选取了聚合物溶液（粘弹性流体）和液晶聚合物溶液，利用激光多普勒测速仪（LDV）对聚合物溶液在矩形收缩通道和矩形膨胀通道中的启动流动进行了测量。并进行了流场显示实验。此外，对粘弹性起动流进行了数值研究。结果表明，在收缩和膨胀附近的流动是三维的，粘弹性流体的流动行为比牛顿流体复杂。数值模拟结果表明，聚合物溶液在收缩和膨胀附近的行为与聚合物溶液的拉伸性质有关。用羟丙基纤维素（HPC）水溶液涂布流动形成的薄膜，观察到液晶（5CB）的均匀表面排列。研究结果表明，流动诱导的HPC分子的异位取向是5CB表面均匀排列的原因。此外，自制了一台单轴拉伸流变仪，测量了聚丙烯酰胺水溶液的单轴拉伸粘度的增长。

We considered flows in which elongational property of complex fluids played an important part. In the present study, we chose polymer solutions (viscoelastic fluid) and liquid crystalline polymers from many complex fluids.In the study of the flow of polymer solutions, velocity measurement of start-up flow in both a rectangular contraction channel and a rectangular expansion channel was carried out using a laser Doppler velocimeter (LDV). Experiment on flow visualization was also carried out. In addition, viscoelastic star-up flow was numerically investigated. The results indicated that the flow near the contraction and expansion was three-dimensional and the flow behavior of viscoelastic fluids was more complex than that of Newtonian fluids. The results of the numerical simulation showed that the behavior near the contraction and expansion related to the elongational property of polymer solutions.In study of flow of liquid crystalline polymers, coating flow, one of elongational flows, was investgated. Homogeneous surface alignment of liquid crystals (5CB) was observed for films formed by coating flow with aqueous solutions of hydroxypropylcellulose (HPC). The results of the present study suggested that the flow-induced anisortopic orentation of HPC molecules is responsible for the homogeneous surface alignment of 5CB.Moreover, a filament-stretching rheometer was made, and growth of the uniaxial elongational viscosity aqueous solution of polyacrylamide was measured.