Achieving Theoretical Property Limits in Polymer Nanofibers: Stiffness, Strength and Thermal Conductivity

该奖项的目的是确定纳米级聚合物纤维样品的热性能和机械性能能够达到理论极限的程度。尽管聚合物材料的机械性能相对较差，导热性较低，但它们仍被用于数以百万计的消费品中。这是因为长分子链往往是无序的。然而，由于其碳-碳骨架结构，聚合物的固有刚度、强度和导热性都很高。利用超高拉伸比技术，现在可以制造出高度有序的聚乙烯纳米纤维。这项工作将采用微机械步进电机来测试超拉伸聚合物的机械性能。对于热导率测量，将使用最近开发的六线平台。这项工作的好处在于，它将使聚合物纳米纤维的许多应用评估成为可能。有可能达到接近理论极限的性能，因为超拉伸纤维是高度有序的。同时，高刚度、高强度和高导热系数值将刺激广泛的研究。这将在制造技术，如大规模的纳米纤维生产，并在应用，如散热器，热交换器，防弹衣和复合材料。在教育方面，调查人员将扩大卡内基梅隆大学的两门课程。一门课程将重点介绍纳米尺度样品的力学和测试方法。第二个将侧重于热性能和开发超材料的方法来控制它们。研究者的本科课程将通过讲座和便携式“芯片课堂”系统向学生介绍微机械设备。6-9年级的学生将学习通过图标驱动界面对微机械设备进行编程。一名博士生和两名硕士论文学生将获得机械和热测量技术方面的专业知识。

The objective of this award is to determine the degree to which the thermal and mechanical properties of nanoscale polymer fiber specimens can attain theoretical limits. Polymer materials are used in millions of consumer products even though their mechanical properties are relatively poor and their thermal conductivity is low. This is because long molecular chains tend to be disordered. However, the intrinsic stiffness, strength and thermal conductivity of polymers are high due to their carbon-carbon backbone. Using an ultra-high draw ratio technique, it now is possible to fabricate polyethylene nanofibers with a high degree of order. The approach in this work will be to employ a micromachined stepper motor to test ultra-drawn polymer mechanical properties. For the thermal conductivity measurements, a recently-developed six wire platform will be used.The benefit of this work is that it will enable assessment of polymer nanofiber for many applications. It is possible that properties near theoretical limits will be attained because the ultra-drawn fibers are highly ordered. Simultaneous high stiffness, strength and thermal conductivity values will in turn stimulate broad research. This will be in manufacturing techniques such as large scale nanofiber production, and in applications such as heat sinks, heat exchangers, body armor and composites. With regard to education, the investigators will expand two courses at Carnegie Mellon University. One will focus on mechanics and test methods of nanoscale specimens. The second will focus on thermal properties and develop metamaterial approaches to control them. Students in the investigators undergraduate course will be introduced to micromachined devices through a lecture and a portable "Class on a Chip" system. Grade 6-9 students will learn to program a micromachined device through an icon-driven interface. A Ph.D. student and two Master's Thesis students will gain expertise in both mechanical and thermal measurement techniques.