Vibration-Induced Deagglomeration and Shear-Induced Alignment of Carbon Nanotubes in Air

Carbon nanotubes (CNTs) are widely known to agglomerate into difficult to separate, 10-100 mu m bundles, even after suspension in solution. Here, a dry and rapid (approximate to 10 s) method to deagglomerate bulk, unbound multi-walled CNT bundles due to surface acoustic waves (SAW) in a piezoelectric substrate is reported for the first time. The process first forms 1-mu m CNT bundles from extremely large (approximate to 10 Mm/s(2)) mechanical accelerations due to the SAW; these bundles are consequently susceptible to SAW-induced evanescent, quasistatic electric fields that couple into the bundles and form a mat of long (1-10 mu m) individual CNTs on the substrate surface. These CNTs may then be aligned along the direction of shear provided by sliding a glass cover slip 10 mm across the CNT mat. This alignment is notably independent of the SAW propagation direction. Further, the intrinsic structure of the nanotubes is unaffected as verified using Raman spectroscopy. Uniquely simple, the approach avoids the many shortcomings of other CNT deagglomeration techniques-particularly surface modification and suspension in solution-to rapidly separate and align large numbers of CNTs, thereby overcoming a key limitation in their use for a diverse range of applications.