Assessing the temporal stability of surface functional groups introduced by plasma treatments on the outer shells of carbon nanotubes

Abstract

Plasma treatments are emerging as superior efficiency treatment for high surface to volume ratio materials to tune functional group densities and alter crystallinity due to their ability to interact with matter at the nanoscale. The purpose of this study is to assess for the first time the long term stability of surface functional groups introduced across the surface of carbon nanotube materials for a series of oxidative, reductive and neutral plasma treatment conditions. Both plasma duration dose matrix based exposures and time decay experiments, whereby the surface energy of the materials was evaluated periodically over a one-month period, were carried out. Although only few morphological changes across the graphitic planes of the carbon nanotubes were found under the uniform plasma treatment conditions, the time dependence of pertinent work functions, supported by Raman analysis, suggested that the density of polar groups decreased non-linearly over time prior to reaching saturation from 7 days post treatment. This work provides critical considerations on the understanding of the stability of functional groups introduced across high specific surface area nano-materials used for the design of nano-composites, adsorptive or separation systems, or sensing materials and where interfacial interactions are key to the final materials performance.

Nanoporous Atomically Thin Graphene Membranes for Desalting and Dialysis Applications

“…Further increase in oxygen‐plasma time increases the intensity of the D peak along with broadening and distinct changes in the 2D peak. These features are consistent with the formation of a mix of sp 2 and sp 3 bonds (see Figure S4, Supporting Information) caused by: i) damage/attack from free radicals in the plasma, and ii) functionalization of dangling bonds with oxygen as reported by Zandiatashbar et al An increase in oxygen‐plasma time beyond 30 s does not cause significant change in the Raman spectrum except for a decrease in signal intensity, which could potentially arise from aggressive etching that leaves less material to interact with the laser . High‐resolution scanning transmission electron microscopy (STEM) images of graphene with 75 s of plasma etch confirm the presence of sub‐nanometer to nanometer‐sized pores in the hexagonal graphene lattice (Figure B,C; red arrows indicate created pores; also see Figure S5, Supporting Information, for pore size distribution), consistent with the Raman spectra in Figure A.…”

Role of nitrogen–oxygen plasma functionalization of carbon nanotubes in epoxy nanocomposites

“…The chemical functionalization by plasma has the advantages of being fast and solvent‐free, while still allowing a wide variety of chemical modifications . However, the discharging parameters such as pressure, power and time must be controlled to avoid breakage or damage to nanoparticle structures .…”

Surface functionalization of carbon fibers with active screen plasma

“…This behavior was observed in other materials, mainly polymers, although the rate of decay depended on the nature of the substrate, the plasma treatment conditions, and the aging environment. [31][32][33][34] In general, the change in chemistry and properties of the plasma functionalized surfaces is attributed to two factors, namely, surface oxidation upon reaction with atmospheric oxygen and surface adaptation through diffusion of surface species in the bulk, 35,36 although the latter mechanism is assumed to be negligible for carbon substrates.…”