Rheo-X-Ray Investigation of Structure Development in Polymer Melts Under Uniaxial Extensional Flow

ARRA声明：该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。流场强烈扰乱聚合物分子尺度结构的能力具有深远的科学和技术影响。聚合物的非线性流变性直接归因于聚合物分子在流动中的拉伸和排列。内部结构更复杂的材料？聚合物共混物，有序嵌段共聚物，聚合物纳米复合材料，例如？展示更引人注目的流-结构耦合模式。此外，聚合物技术常常依赖于加工过程中流场赋予产物分子或微观结构各向异性的能力。x射线散射是流动和加工过程中原位结构研究的有力工具。然而，迄今为止，x射线散射方法从未应用于定义良好的均匀拉伸流。由于拉伸流动涉及流体元素的指数拉伸，因此在诱导分子或微观结构排列方面，拉伸流动比剪切流动明显更有效。这些相同的特性使得在实验室测试中产生均匀的拉伸流非常困难。在这个项目中，西北大学的研究人员将开发出独特的仪器，首次实现基于同步加速器的原位研究，研究明确的单轴拉伸流中聚合物结构的发展。这个实验将建立在一个经过验证的，商业上可用的测试夹具，旨在促进使用传统旋转流变仪的拉伸流变。对于同步加速器研究，该夹具将集成到一个带有计算机运动控制和定制的对流烤箱的测试平台中，旨在促进x射线进入小角度和广角x射线散射。这种仪器将为几乎每一类聚合物材料的科学探究开辟新的前景，这些材料一直是流动诱导结构研究的对象。在这个项目中，将探索三个具体的应用领域：(i)有序嵌段共聚物的排列；（ii）聚合物纳米复合材料中的粒子取向；(3)半结晶聚合物的流动诱导结晶。非技术概要庞大的塑料材料工业在很大程度上取决于纤维纺丝、挤压和成型等过程中引起的分子结构变化，这些变化对最终产品达到预期性能至关重要。美国西北大学的研究人员将在阿贡国家实验室的先进光子源上使用强大的x射线，开发一种独特的新仪器，使这些分子尺度的结构变化能够被研究。拉伸流? ?熔融塑料被拉伸的方式与太妃糖被拉伸的方式大致相同。极亮的x射线束将促进实时？纳米尺度结构动力学的测量在广泛的高性能材料。此外，根据该提案开发的仪器将提供给全国各地的研究人员，从而为美国的科学基础设施做出永久的贡献。

ARRA STATEMENT:This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARY The ability of flow fields to strongly perturb molecular-scale structure in polymers has profound scientific and technological consequences. The nonlinear rheology of polymers is directly attributed to stretching and alignment of polymer molecules under flow. Materials with more complex internal structure?polymer blends, ordered block copolymers, polymer nanocomposites, for example?exhibit even more dramatic modes of flow-structure coupling. Further, polymer technology frequently hinges on the ability of flow fields during processing to impart molecular or microstructural anisotropy in the resulting product. X-ray scattering is a powerful tool for in situ structural studies during both flow and processing. To date, however, x-ray scattering methods have never been applied to well defined, homogenous extensional flows. Since extensional flows involve exponential stretching of fluid elements, they are dramatically more effective than shear flows at inducing molecular or microstructural alignment. These same characteristics make it notoriously difficult to produce homogenous extensional flows for laboratory testing. In this project, researchers at Northwestern will develop unique instrumentation that will allow, for the first time, in situ synchrotron-based studies of polymer structure development in well-defined uniaxial extensional flow. This experiment will be built around a proven, commercially available test fixture designed to facilitate extensional rheometry using conventional rotational rheometers. For synchrotron studies, this fixture will be integrated into a testing platform with computerized motion control and a custom-fabricated convection oven designed to facilitate x-ray access for both small- and wide-angle x-ray scattering. This instrumentation will open new vistas of scientific inquiry in virtually every class of polymer material that has been the object of flow-induced structure studies. Within this project, three specific application areas will be explored: (i) alignment of ordered block copolymers; (ii) particle orientation in polymer nanocomposites; and (iii) flow-induced crystallization of semi-crystalline polymers.NON-TECHNICAL SUMMARYMuch of the vast plastic materials industry hinges upon changes in molecular structure induced in processes such as fiber spinning, extrusion and molding, that are essential to achieve the desired performance in the end product. Using powerful x-rays at the Advanced Photon Source at Argonne National Laboratory), researchers from Northwestern University will develop a unique new instrument that will enable these molecular-scale structural changes to be studied in ?extensional flow?? flows in which molten plastics are stretched much in the same way that taffy is pulled. Extremely bright x-ray beams will facilitate ?real-time? measurements of nanometer-scale structural dynamics in a wide range of high-performance materials. Further, the instrumentation developed under this proposal will be made available to researchers across the country, thus making a permanent contribution to US scientific infrastructure.