Fabrication of Freeform Hierarchical Micro/Nanostructures by Control of Capillary Interactions with Aligned Carbon Nanotubes

尽管个别碳纳米管（CNT）的优良性能，它们的性能作为组件通常是穷人，由于低的包装密度，即使当它们自组装，以创建垂直对齐？森林？在成长过程中。 这使得目前的CNT森林不足以用于大多数MEMS器件应用，并且还在很大程度上阻止了它们与传统微制造的后处理的兼容性。该项目将通过创建一种新的制造工艺来克服CNT在微制造中使用的障碍，该工艺用于由对齐的CNT制成的坚固且复杂的三维微结构。 该过程包括通过热化学气相沉积生长CNT森林，然后使用毛细管力控制CNT的致密化。 由于毛细力可以单独渗透CNT森林微结构，因此该过程可以并行地产生各种各样的形状。从我们最近的演示中得出的结论？毛细血管形成在这一过程中，我们将：（1）对原型CNT形状库的毛细管形成进行严格的实验，并以无量纲化的方式将结果与CNT结构特征相关联;（2）创建将动态液体-蒸气界面处的自由能平衡与CNT森林的变形相耦合的有限元模型，并将模型结果与实验进行比较;（3）通过纳米压痕测量自由形式的CNT结构的机械性能;和（4）产生和测试聚合物涂覆的和金属涂覆的CNT杠杆，以用作各向异性润湿表面和微弹簧接触。知识价值将来自于我们对如何设计CNT的稳健自由形式结构的理解，以及更广泛地对表面张力和弹性力之间的平衡如何支配纤维网络的组织的理解。 这些见解将涉及自然系统中的自组装，并将适用于其他纳米结构材料。 我们将通过以下方式将我们的研究结果与多个学科的广泛受众联系起来：少数民族本科生和研究生参与研究;涉及CNT生长和毛细血管形成的新本科实验室实验;以及与艺术家和建筑师合作创建结构模型和展览。

Despite the excellent properties of individual carbon nanotubes (CNTs), their properties as assemblies are typically poor due to the low packing density even when they are self assembled to create vertically aligned ?forests? during growth. This renders current CNT forests inadequate for most MEMS device applications, and also largely prevents their compatibility with post-processing by traditional microfabrication. This project will overcome the barrier to use of CNTs in microfabrication by creating a new manufacturing process for robust and complex three dimensional microstructures made of aligned CNTs. This process consists of growth of CNT forests by thermal chemical vapor deposition, followed by controlled densification of the CNTs using capillary forces. Because capillary forces can infiltrate CNT forest microstructures individually, this process can create a wide variety of shapes in parallel. Building from our recent demonstration of this ?capillary forming? process, we will: (1) perform rigorous experiments on capillary forming of a library of archetypal CNT shapes, and relate the results to CNT structural characteristics in a nondimensionalized fashion; (2) create a finite element model that couples the free energy balance at a dynamic liquid-vapor interface to the deformation of a CNT forest, and compare the model results to experiments; (3) measure their mechanical properties of the freeform CNT structures by nanoindentation; and (4) create and test polymer-coated and metal-coated CNT cantilevers for application as anisotropic wetting surfaces and microspring contacts. Intellectual merit will result from our understanding of how to engineer robust freeform structures of CNTs, and more broadly of how a balance between surface tension and elastic forces governs the organization of fibrous networks. These insights will relate to self-assembly in natural systems and will be applicable to other nanostructured materials. We will connect our findings to broad audiences across multiple disciplines through: involvement of minority undergraduate and graduate students in research; a new undergraduate laboratory experiment involving CNT growth and capillary forming; and by creating structural models and exhibits in collaboration with artists and architects.