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

纤维常与塑料混合，使其更硬、更强或更好的导电体。然而，这种含纤维的塑料复合材料很难通过标准成型或其他加工方法制造出来。此外，纤维在制造过程中经常受到损坏。该项目旨在创建一个桥接系统，将颗粒填料转化为可重组纤维网络，即纤维在断裂后能够重新组装。具有这种网络的复合材料可以保持最初的设计性能（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，特别是在匹兹堡科技高中和两所少数民族入学率高的K-8学校，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，并通过湿润流体的半月板将它们桥接在一起来实现。由于半月板在流动过程中不断断裂和重组，复合材料具有优异的加工性能。聚合物复合材料的性能可以通过选择合适的填料来调整，该项目将测试实现高刚度、高韧性或高导电性复合材料的填料。该假设将以聚苯乙烯作为基体塑料，二氧化硅或金属颗粒作为颗粒填料进行实验验证。将使用各种热塑性材料作为湿润阶段，在颗粒之间形成半月板。聚苯乙烯、颗粒和湿相将通过优化的熔融挤出工艺混合，以实现颗粒的半月板桥接。表征包括拉伸和冲击测试，电导率测量，以及扫描电子显微镜的形态学研究。这个项目的智力意义在于证明半月板桥接可以被利用来获得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.