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

尽管单个碳纳米管（CNTs）具有优异的性能，但它们作为组件的性能通常很差，因为它们的包装密度低，即使它们自组装以形成垂直排列的“森林”时也是如此。在增长。这使得目前的碳纳米管森林不适用于大多数MEMS器件应用，并且也在很大程度上阻碍了它们与传统微加工后处理的兼容性。该项目将通过创建一种新的制造工艺来制造由对齐的碳纳米管制成的坚固而复杂的三维微结构，从而克服在微制造中使用碳纳米管的障碍。该过程包括通过热化学气相沉积生长碳纳米管森林，然后使用毛细力控制碳纳米管的致密化。由于毛细管力可以单独渗透到碳纳米管森林的微观结构中，这个过程可以平行地产生各种各样的形状。根据我们最近的演示？毛细管形成?过程中，我们将：(1)对原型碳纳米管形状库的毛细管形成进行严格的实验，并以非量纲化的方式将结果与碳纳米管的结构特征联系起来；(2)建立了将动态液汽界面的自由能平衡与碳纳米管森林变形耦合的有限元模型，并将模型结果与实验结果进行了比较；(3)采用纳米压痕法测量自由曲面碳纳米管结构的力学性能；(4)创建和测试聚合物涂层和金属涂层碳纳米管悬臂梁，用于各向异性润湿表面和微弹簧接触。知识价值将产生于我们对如何设计坚固的碳纳米管自由结构的理解，以及更广泛地说，表面张力和弹性力之间的平衡如何控制纤维网络的组织。这些见解将与自然系统中的自组装有关，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发现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；一个新的涉及碳纳米管生长和毛细管形成的本科生实验室实验；通过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.