Carbon-nanotube foams, forests, and turfs have received growing attention as they appear to very promising in such applications as energy-mitigating thin films, cold cathode arrays, low-reflectance coatings, and contact thermal switches, to name a few. To ensure proper functionality of these materials in operation, it is critical to assess their lifetime, that is, tolerance to mechanical degradation.

Now, in new work published this month, Julia Greer and colloborators at Caltech performed uniaxial compression studies on 50-μm-diameter bundles of thousands of nominally vertical, intertwined carbon nanotubes grown via chemical vapor deposition from a photolithographically defined catalyst. These experiments led the authors to discover that the characteristic bottom-to-top sequential buckling proceeds by first nucleating on the bundle surface and then propagating laterally through the bundle, gradually collapsing the entire structure. This mechanism accounts for all significant deformation accommodation. The researchers also examined the inhomogeneous microstructure, demonstrating density and tube orientation gradients that they believe play a role in the unique periodic buckling deformation mechanism.