NSF Young Investigator

西北大学P.I: Wesley Burghardt我在西北大学的研究小组的中心主题是复杂流体中流动引起的微观结构变化，由此产生的机械流变行为，以及非线性流变在更复杂流体力学问题中的后果之间的关系。在NYI的支持下，我们将开展三个项目：(i)嵌段共聚物溶液的流动诱导对准。有序嵌段共聚物具有两个结构层次的复杂性。分子弛豫反映在粘弹性行为中。然而，聚合物自组装成有序的微观结构（如片层）使得结构和流变性能都具有高度的各向异性。我们将利用流动双折射研究流动下宏观取向的发展，并结合力学测试研究平均取向状态对体流变行为的影响。（ii）高度纠缠聚合物的本构不稳定性。我们将研究两类材料，其中本构行为已被提出服从应力对变形的不稳定非单调依赖。高度纠缠的聚合物溶液将在阶梯应变中进行研究，而所谓的活性聚合物（胶束表面活性剂溶液）将在稳定剪切流动中进行研究。在这两种情况下，我们将利用我们实验室开发的光学方法，使用应力-光学规则来研究完全应力张量。（三）非牛顿流体力学。实验研究将在复杂几何形状的粘弹性聚合物溶液中进行。这些努力旨在开发一个实验数据库，用于测试粘弹性流动的数值模拟，并区分竞争的本构模型。

ABSTRACT CTS-9457083 Northwestern University P.I.: Wesley Burghardt The central theme of research in my group at Northwestern in the relationship between flow-induced microscopic structural changes in complex fluids, the resulting mechanical rheological behavior behavior, and further, the consequences of nonlinear rheology in more complex fluid mechanical problems. Under NYI support, we will pursue three projects, (i) Flow-induced alignment in block copolymer solutions. Ordered block copolymers are characterized by complexity at two structural levels. Molecular relaxations are reflected in viscoelastic behavior. However, the self-assembly of the polymers into ordered microstructures (such as lamellae) renders both structure and rheological properties highly anisotropic. We will use flow birefringence to study the development of macroscopic alignment under flow, coupled with mechanical testing to study how bulk rheological behavior is affected by the average orientation state. (ii) Constitutive instabilities in highly entangled polymers. We will investigate two classes of materials where the constitutive behavior has been proposed to be subject to an unstable nonmonotonic dependence of stress on deformation. Highly entangled polymer solutions will be studied in step strain, while so called living polymers (micellar surfactant solutions) will be studied in steady shear flow. In both cases, we will utilize optical approaches developed in our laboratory for studying the complete stress tensor using the stress-optical rule. (iii) Non-newtonian fluid mechanics. Experimental studies will be conducted on well-characterized viscoelastic polymer solutions in complex geometries. These efforts are directed towards developing an experimental database with which to test numerical simulations of viscoelastic flow, and discriminate among competing constitutive models.