Shear and Extensional Rheology of Nanoclays and Nanotubes in Polymer Melts and Solutions

这笔赠款用于全面表征纳米粘土/聚合物和碳纳米管/聚合物复合材料在剪切和拉伸方面的非线性流变学、颗粒取向和结构发展，以及开发用于控制和优化纳米复合材料工艺的模拟工具。聚合物纳米复合材料表现出显著增强的性能，包括增加的强度、刚性、阻隔性和耐热性，而冲击强度没有显著损失。两种类型的纳米颗粒，自然形成的层状纳米粘土和合成的碳纳米管，在改善热塑性和热固性聚合物的机械和电学性能方面显示出希望。然而，这些改进也伴随着加工成本：观察到少量添加高表面积与体积比的纳米粘土和纳米管可以显著增加聚合物熔体和溶液的粘度和弹性，使聚合物纳米复合材料产品的挤出和注射成型变得复杂。此外，加工对纳米颗粒取向和结构发展的影响，以及产品材料的性能特性，还没有被很好地理解。通过提出的聚合物纳米复合材料的综合流变和结构表征，将解决以下问题：填充了极大长径比纳米颗粒的熔体和溶液的剪切和拉伸粘度是多少？它们对不同长径比的管子和圆盘的纳米颗粒几何形状有什么依赖关系？剪切和伸展流动中的颗粒取向和结构发展是什么？可以为应力/应变/结构的过程建模开发哪些模型？纳米颗粒在多大程度上会在伸展流动中排列？纳米管和纳米粘土的弹性性质与聚合物熔体和溶液的粘弹性、纳米颗粒浓度与溶液的粘弹性性质、取向和结构发展与粘弹性性质之间的关系是什么？纳米粒子在拉伸和剪切时的流动对准特性是什么，管子和血小板是否具有非常不同的流动对准结构？

This grant provides funding for the comprehensive characterization of the non-linear rheology, particle orientation, and structure development of nanoclay/polymer and carbon nanotube/polymer composites, in both shear and elongation, and the development of simulation tools for control and optimization of processes for nanocomposites. Polymer nanocomposites exhibit significantly enhanced performance properties, including increased strength, stiffness, barrier properties, and heat resistance, without a significant loss in impact strength. Two types of nanoparticles, naturally occurring layered nanoclays and synthesized carbon nanotubes, show promise in improving the mechanical and electrical properties of thermoplastic and thermoset polymers. However, these improvements come with a cost in processing: small additions of the high surface-area-to-volume-ratio nanoclays and nanotubes have been observed to significantly increase the viscosity and elasticity of polymer melts and solutions, complicating the extrusion and injection molding of polymer nanocomposite products. In addition, the effect of processing on nanoparticle orientation and structure development, and hence performance properties of the product materials, is not well understood. With the proposed comprehensive rheological and structural characterization of polymer nano-composites, questions such as the following will be addressed: What are the shear and extensional viscosities of melts and solutions filled with extremely large aspect ratio nanoparticles? What are their dependencies on nanoparticle geometry, varying between tubes and discs of different aspect ratios? What is the particle orientation and structure development in shear and extensional flow? What models can be developed for process modeling of stress/strain/structure? To what degree do nanoparticles become aligned in an extensional flow? What are the correlations between elastic properties of nanotubes and nanoclays and the viscoelasticity of the polymer melts and solutions, between nanoparticle concentration and viscoelastic properties of solutions, between orientation and structure development and viscoelastic properties? What are the flow-aligning properties of the nanoparticles in extension and shear, and do the tubes and platelets have very different flow-aligning structures?