Collaborative Research: Wetting Phenomena in Particle-Filled Polymers: Multifunctional Composites with Easy Processability

纤维经常被混入塑料中，使它们更硬，更强，或更好的电导体。然而，这种含纤维的塑料复合材料难以通过标准模制或其它加工来制造。此外，纤维在制造过程中经常受到损坏。该项目旨在创建一种桥接系统，将颗粒填料转化为可重整纤维网络，即断裂后能够重新组装的纤维。 具有这种网络的复合材料可以保持初始设计性能（如高强度和韧性或高导电性），而不会在加工过程中遭受性能损失。 主要研究人员将在大学预科阶段进行科学推广，特别是在匹兹堡理工高中和两所少数民族入学率高的K-8学校，以鼓励学生接受STEM学科的教育。本研究的具体假设是，含有纤维状不稳定填料的复合材料可以通过将固体颗粒分散到聚合物基体中来实现，并通过润湿流体的润湿将它们桥接在一起。由于纤维在流动过程中不断断裂和改革，复合材料将具有优良的加工性能。所得到的聚合物复合材料的性能可以通过适当选择填料来定制，并且该项目将测试实现具有高刚度或高韧性或高导电性的复合材料的填料。将使用聚苯乙烯作为基质塑料，二氧化硅或金属颗粒作为颗粒填料，对该假设进行实验测试。各种热塑性材料将被用作在颗粒之间形成粘性的润湿相。聚苯乙烯、颗粒和润湿相将通过优化的熔融挤出工艺共混，以实现颗粒的交联桥接。表征包括拉伸和冲击测试，电导率测量，并通过扫描电子显微镜进行形态学研究。该项目的智力意义在于证明，可以利用微球桥接来实现具有普通颗粒填充聚合物的可加工性、具有纤维增强复合材料的机械性能或接近金属的导电性的材料。此外，该项目将推进填充聚合物中毛细管相互作用的基础知识。

Fibers are often mixed into plastics to make them stiffer, stronger, or better electrical conductors. Yet such fiber-containing plastic composites are difficult to manufacture by standard molding or other processing. Furthermore, fibers often suffer damage during manufacturing. This project is to create a bridging system that converts particle fillers into a network of reformable fibers i.e. fibers that are capable of reassembling after breaking. Composites with such network can retain the initial design properties (such as high strength and toughness or high conductivity) without suffering property loss during processing. The Principle Investigators will conduct scientific outreach at pre-college level, especially at the Pittsburgh SciTech High School and two K-8 schools with high minority enrollment, to encourage students to pursue education in STEM disciplines.The specific hypothesis of this research is that composites containing a fiber-like labile filler can be realized by dispersing solid particles into a polymer matrix, and bridging them together by menisci of a wetting fluid. Since the menisci continuously break and reform during flow, the composites will have excellent processability. The properties of the resulting polymer composites may be tailored by suitable choice of filler, and this project will test fillers that realize composites with high stiffness, or high toughness, or high electrical conductivity. The hypothesis will be tested experimentally using polystyrene as the matrix plastic, and silica or metal particles as the particulate filler. Various thermoplastic materials will be used as the wetting phase that forms menisci between particles. Polystyrene, particles, and the wetting phase will be blended by a melt extrusion process optimized to realize meniscus-bridging of particles. Characterization includes tensile and impact testing, electrical conductivity measurements, and morphological studies by scanning electron microscopy. The intellectual significance of this project is to demonstrate that meniscus-bridging can be exploited to achieve materials with the processability of ordinary particle filled polymers, with the mechanical properties of fiber reinforced composites, or the electrical conductivity approaching metals. Furthermore, this project will advance the fundamental knowledge of capillary interactions in filled polymers.