Tribology of Polymer Nanocomposites

0099649 Sawyer该SGER奖将支持一项关于纳米颗粒增强聚合物摩擦学应用效果的可行性研究。 有强有力的迹象表明，与传统的填充聚合物相比，用硬纳米粒子填充的聚合物将表现出显著的摩擦学性能改善。 聚合物广泛用于轴承应用，因为它们提供安静的连续操作，具有低摩擦系数，吸收振动，对配合面具有顺应性和非磨损性，可以容易地制造，廉价，无腐蚀性，并且通常具有生物相容性。 设计均质聚合物材料轴承的挑战在于其低耐磨性（高磨损率）。 为了提高耐磨性，经常添加硬质填料颗粒，然而这些硬质填料颗粒增加了对配合面的磨粒磨损，并增加了摩擦的滑动系数。 润滑填料也被添加到聚合物中，并且在某些操作条件下可以降低磨损率和摩擦系数，但是必须在磨损表面处持续供应润滑填料，并且这些材料通常对环境敏感。 聚合物的理想填料应该是惰性的、增强的、非研磨性的，并且降低摩擦系数。 有充分的证据表明，纳米颗粒填充的聚合物可能是这种“理想”的复合材料。例如，最近的研究表明，在聚合物复合材料中填充硬质纳米颗粒可以提高耐磨性，同时减少对体的磨损，降低滑动摩擦系数。 这类摩擦学行为将对聚合物轴承产生影响，其范围涵盖从需要干式滑动轴承的工业应用到矫形植入材料，再到空间环境中的自润滑轴承。然而，为了设计具有最佳性能和预期性能的复合材料，必须克服一些严重的限制。 首先，我们对填充聚合物的磨损机制的理解很差。 例如，填料/基体界面的作用和颗粒尺寸的影响还没有得到很好的研究，也没有考虑填料界面或尺寸的合适模型。其次，对于非润滑纳米颗粒，降低摩擦系数的机制尚不清楚。 最后，尽管有强有力的证据表明纳米颗粒填充聚合物在性能上有很大的改进，但还没有对纳米颗粒填充聚合物的磨损应用进行全面的研究。该项目的总体科学目标是通过以下方法对填充聚合物的磨损机理有一个基本的了解：a）实验性地分离颗粒尺寸的影响（10 nm至10微米），颗粒纵横比（1至1000）、分散、填料/基质界面和基质性能对性能的影响，以及2）获得磨损行为与其他机械性能之间相关性的参数理解，3）磨损特性的建模。*

0099649SawyerThis SGER award will support a feasibility study of the effect of nanoparticle strenghthening of polymers for tribological applications. There are strong indications that polymers filled with hard nanoparticleswill exhibit significant improvements in tribological performance ascompared to traditional filled polymers. Polymers are widely used inbearing applications because they provide quiet continuous operation, have alow coefficient of friction, absorb vibrations, are compliant andnon-abrasive to the counterface, can be easily manufactured, areinexpensive, non-corrosive, and are generally biocompatible. The challengein designing bearings with homogeneous polymeric materials is their low wearresistance (high wear rates). Hard filler particles are frequently added toimprove the wear resistance, however these hard filler particles increasethe abrasive wear to the counterface and increase the sliding coefficient offriction. Lubricious fillers are also added to polymers and under certainoperating conditions can reduce the wear rate and the coefficient offriction, however a constant supply of lubricous filler must be available atthe wear surface and these materials are frequently sensitive to theenvironment. The ideal filler for polymers would be inert, reinforcing,non-abrasive, and reduce the coefficient of friction. There is goodevidence that nanoparticle filled polymers may be this 'ideal' composite.For example, recent studies have shown that the wear resistance can increasein polymer composites filled with hard nanoparticles, while at the same timethe wear of the counterbody decreases and the sliding coefficient offriction decreases. This type of tribological behavior will have an impactin polymeric bearings covering the spectrum from industrial applicationsneeding dry sliding bearings, to orthopaedic implant materials, toself-lubricating bearings for space environments.In order to design composites with the optimum properties and predictperformance, however, some severe limitations must be overcome. First, ourunderstanding of the mechanisms contributing to wear performance in filledpolymers is poor. For example, the role of the filler / matrix interfaceand the effect of particle size has not been well studied nor are thereappropriate models that consider the interface or size of the filler.Secondly, it is unclear for non-lubricious nanoparticles what the mechanismis that lowers the coefficient of friction. Finally, nanoparticle filledpolymers have not comprehensively explored for wear applications despite thestrong evidence suggesting large improvements in performance.The overall scientific goal of the project is to gain a fundamentalunderstanding of the wear mechanisms in filled polymers by a) experimentallyisolating the effects of particle size (10 nm to 10 micrometers), particleaspect ratio (1 to 1000), dispersion, filler / matrix interface, and matrixproperties on performance, and 2) obtaining a parametric understanding ofthe correlation between wear behavior and other mechanical properties, 3)modeling of the wear properties.***