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

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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.