Squeezing Flow of Functional Fluids in Narrow Gaps

对液晶聚合物（LCP）溶液在两个平行窄间隙圆平板间的径向流动和随后的挤压流动进行了实验研究。在稳定径向流停止并暂停一段时间后，开始挤压流。测量了与液膜传递的力，同时观察了测试流体的流向模式。澄清以下几点。(1)在挤压运动相同的情况下，预剪切变形（径向流）的强度对流体的流向模式和传递力有很大的影响。(2)暂停时间对挤压流动也有类似的影响。(3)以上结果表明，流场历史效应将控制LCP的走向模式和功能。(4)在弱剪切前流的情况下，用Carreau模型对LCP的挤压流进行了近似估计。我们还研究了向列液晶（LC）在窄间隙中的挤压流。在第一阶段，研究了电场作用下二维泊泽维尔流中LC在50-100mm窄间隙内的特性。随着电场的增加，LC的最大表观粘度比无电场时大4 - 5倍，这种ER效应与电场强度的平方成正比。利用上述结果估计LC挤压流中的ER效应表明，由于随着间隙尺寸的减小，电场强度的增加抵消了粘度剪切变薄的影响，因此预计挤压流中的ER效应是恒定的。

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.