Squeezing Flow of Functional Fluids in Narrow Gaps

本文对液晶高分子溶液在两平行窄缝圆平板间的径向流动及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。测量与液膜一起传递的力，同时观察测试流体的流动对准图案。澄清以下几点。(1)即使挤压运动是相同的，预剪切变形（径向流）的强度对流动排列模式和传递力有很大的影响。(2)停顿时间对挤压流也有类似的影响。(3)上述结果表明，LCP的取向模式和功能将受到流动历史效应的控制。(4)在弱预剪切流的情况下，用Carreau模型近似估计了液晶的压缩流，并研究了窄缝中液晶的压缩流。在第一阶段，在50- 100 mm的窄间隙中，研究了电场作用下二维Poiffille流中的LC特性。电场增加的LC的最大表观粘度比没有电场时大4至5倍，并且该ER效应与电场强度的平方成比例。利用上述结果对液晶挤压流动中的电流变效应进行了估计，结果表明，随着差距尺寸的减小，电场强度的增加抵消了粘度剪切变稀的影响，挤压流动中的电流变效应是恒定的。

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.