Squeezing Flow of Functional Fluids in Narrow Gaps

对液晶聚合物溶液在两个平行的窄间隙圆形平板之间的径向流动和随后的挤压流动进行了实验研究。在停止稳定的径向流动并暂停一段时间后，开始挤压流动。测量与液膜一起传递的力，并同时观察到测试流体的流动对准模式。澄清了以下几点。(1)即使挤压运动相同，预剪切变形(径向流动)的强度对流型和传力也有很大的影响。(2)暂停时间对挤压流的影响也是相似的。(3)上述结果表明，LCP的排列方式和功能将受到水流历史效应的控制。(4)在弱预剪切流的情况下，用Carreau模型近似估计了LCP的压缩流，并研究了向列相液晶在窄间隙中的压缩流。在第一阶段，在50-100 mm的窄间隙内，研究了电场作用下二维Poiseuille流中LC的特性。液晶的最大表观粘度随电场的增加而增大，是不加电场时的4~5倍，电流变效应与电场强度的平方成正比。利用上述结果对LC挤压流中的电流变效应进行了估算，结果表明，在挤压流中，由于剪切稀化效应的影响被电场强度的增大和间隙尺寸的减小所抵消，因此在挤压流中可以预期恒定的电流变效应。

Experimental examination has been conducted on radial flows and the subsequent squeezing flow of liquid crystalline polymer (LCP) solutions between two parallel circular flat plates with a narrow gap. After the steady radial flow was stopped and a pause time is taken, then the squeezing flow is started. Forces transmitted with the liquid film are measured and flow alignment patterns of the test fluids are simultaneously observed. The following points are clarified. (1) Even if the squeezing motion is the same, the intensity of the pre-shear deformation (radial flow) gives great influence on the flow alignment patterns and the transmitted force. (2) The similar influence of the pause time on the squeezing flows is also observed. (3) The above results show that the alignment patterns and the functional of the LCP will be controlled by the flow historical effects. (4) In the case with the weak pre-shear flow, the squeezing flow of the LCP is approximately estimated with the Carreau model.We have also studied a squeezing flow of a nematic liquid crystal (LC) in a narrow gap. At the first stage, characteristics of the LC in a two-dimensional Poiseuille flow under electric fields have been examined in the narrow gap of 50-100mm. A maximum apparent viscosity of the LC,increased by the electric field, is 4 to 5 times larger than with no electric field and this ER effect is in proportion to the square of the electric field strength. Estimation of the ER effect in the squeezing flow of LC utilizing above results shows that constant ER effects are expected in the squeezing flow because the influence of the shear thinning of the viscosity is counterbalanced by the increase of the electric field strength with the decrease in the gap size.