Coiling of Single-Walled Carbon Nanotubes via Selective Topological Fluid Flow: Implications for Sensors

A thin-film microfluidic vortex fluidic device (VFD) housing a rapidly rotating tube inclined at +45° imparts mechanical energy to the liquid, which can be harnessed to gain access to non-equilibrium states of self-assembled nanomaterials. Coiled single-walled carbon nanotubes (SWCNTs) are formed from entangled counterparts in such a dynamic thin film of toluene, and with a recent detailed understanding of the high-shear topological fluid flow of submicron dimensions in the VFD, a systematic study on forming such toroidal structures in immiscible biphasic systems has been undertaken. This involved using mixtures of water and toluene, m-xylene, or p-xylene containing a suspension of SWCNTs and using VFD quartz tubes of different diameters, such as 10, 15, and 20 mm outside diameter (O.D.), along with changing the common hemispherical base of the tube to a flat-base tube as a strategy for decoupling the effect of different topological fluid flows generated in the VFD. Selective control over the diameter of the resulting toroids of SWCNTs down to ca. 35 nm in diameter has been established with the expected SWCNT ring strain in the toroids, as established by Raman spectroscopy, and its application in sensors.