The mechanical response of aligned carbon nanotube mats via transmitted laser intensity measurements

Abstract

Carbon nanotubes are one of the more widely studied nanostructures today, with ongoing attempts to exploit their small size, large aspect ratio, and combination of mechanical, optical, and electronic properties. In this work, a chamber was designed to pass a laser through a mat of aligned carbon nanotubes and monitor the variation in transmitted light intensity in response to different mechanical deformations. This approach specifically takes advantage of the scale and mechanical and optical properties of carbon nanotubes, particularly their high elastic limit and anisotropic light absorption. In this study, we measure the flexural rigidity (the product EI) of carbon nanotube arrays. Vertically aligned nanotubes were grown in periodic arrays, and fluid flow was applied normal to the nanotube axis. These nanotubes deflect due to shear caused by fluid drag, and this deflection is monitored experimentally with high accuracy by measuring a decrease in transmitted light intensity as a function of increasing fluid velocity and density. This response was also simulated, using a model based on the Stokes-Oseen equations with a correction for the small length scales associated with nanotube mats. The experimental deflection data and the estimated force on the tubes from simulations are used for determining the flexural rigidity of CNTs, to be of the order of 10 -15 Nm2. Using this method, we also demonstrate a carbon nanotube-based fluid flow and shear force sensor that offers fast response, repeatability, and that can measure forces in very close proximity to surfaces (such as in boundary layer flow). © 2009 Materials Research Society.