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

of individual isolated MWNTs potentially conferred to the material made from them can be achieved or exploited. [ 2–6 ] Consequently , direct use of nanotubes [ 7–10 ] in their intended application as deagglomer-ated MWNTs for mechanical stiffening and strengthening, conductivity control , [ 11 ] particularly in transparent media for the replacement of indium tin oxide as a nearly depleted resource, [ 12 ] and even respiratory studies [ 13,14 ] would streamline industrial processes and facilitate their broader use—without having to resort to fl uid suspension, surfactants, and substantial processing as is generally required now. [ 15 ] Many researchers have explored selective chemistries and mechanical techniques to obtain debundled CNTs to address the limitations associated with nanotube agglomeration. Selective chemical functionalization has commonly been used to improve the dispersion of the CNTs in different solvents and polymers. For instance, CNT solubility improves in organic solvents once they are covalently endowed with alkene functional groups [ 16–19 ] such as tetrahy-drofuran, chloroform, dimethylformamide, [ 20 ] and methylene chloride. [ 21 ] Ultrasonication and ball milling, on the other hand, are straightforward approaches to break down CNT bundles, though at a cost: ultrasonication over long periods causes a signifi cant increase in defects in the CNTs with an associated increase in the D band intensity (as measured by Raman spec-troscopy) due to disordered sp 3 carbon. [ 22 ] In extreme cases, the graphene layers of the CNTs are completely destroyed and the nanotubes are converted into amorphous carbon nanofi bers. [ 23 ] Furthermore, individual CNTs obtained by wet ultrasonication are usually very short, [ 24 ] only ≈10 to ≈100 nm in length. Ultra-sonication also creates holes along the CNT side walls, resulting in " worm-eaten " damage. [ 25–27 ] Likewise, ball milling creates a large amount of amorphous carbon from CNT samples, [ 28,29 ] clearly indicating that the CNTs are damaged. Once debundled, the orientation of the CNTs is important in most practical applications, and several methods have already been demonstrated to align the individually dispersed CNTs in a liquid medium. Some common methods include shear fl ows, [ 30,31 ] electric fi elds, [ 32–35 ] and magnetic fi elds, [ 36–39 ] all of which have limited alignment effi ciency because of the rotation of CNTs due to fl uid transport and Brownian motion of the CNTs in the fl …