Dewetting assisted self-assembly of carbon nanotube into circular nanorings

Abstract

In this article, we demonstrate how the instability of a polymeric thin film, when cast either as a mobile underlying support-layer of a bilayer assembly, as a mixture, or as a template, affects the self-assembly and arrangement of carbon nanotube (CNT) nanoparticles dispersed over/with it. The interplay of the different forces, like centrifugal, dewetting, Marangoni, electrostatic, assist the mobile nanoparticles in arranging themselves into circular ring-like structures. The congruence of the length scales of the self-assembled circular ring and the dewetted length scales of the thin polystyrene film reveals that the influence of dewetting dynamics is majorly responsible for the incipience of ring formations. However, the absence of coarsening and complete stoppage of movement of the rings towards the particulate region, reveals the presence of electrostatic repulsion. The nanoparticles not involved in circular-ring-self-assembly formation are driven by Marangoni force and engender nano-scratches over the polymeric surface. CNTs of smaller lengths deposit in the particulate zone where also, beyond a particular aspect ratio, the nanotubes are found to bend into circular rings. The bending of the carbon nanotubes is an energetically favored self-organization process controlled by the shape formation energy. When the underlying dewetted polystyrene surface acts as a template, the assembled CNT forms a circular ring-like interconnected relief structure. The circular rings of CNTs formed throughout the PS surface, fabricated by the dewetting of the mixture method, can be used to identify trace amounts of oil from an oil–water mixture by selective adsorption. The different self-assembled ring structures of CNTs are realized only for a specific concentration range of CNTs. The nanotubes assemble into random bundles/blobs devoid of any definite structures above this concentration.