Stabilization of Carbon Nanotubes and Graphene by Tween-80: Mechanistic from and Simulation Studies

Polyoxyethylene sorbitan monooleate is commonly used to obtain stable dispersions of nanoparticles (NPs) such as carbon nanotubes (CNTs) and graphene. However, the mechanism underlying dispersion is poorly understood. The present study aimed at investigating the mechanism of stabilization of carbon NPs (CNPs), namely, single-walled CNTs (SWCNTs), multi-walled CNTs (MWCNTs), and graphene, by Tween-80 using attenuated total internal reflection-Fourier transform infrared and nuclear magnetic resonance (NMR) spectroscopy. Molecular dynamics (MD) simulations were performed to identify, at the atomic scale, the significant interactions that underlie the adsorption and the stabilizing effect of Tween-80 on CNPs, in this way corroborating the spectroscopy results. Spectroscopic analysis revealed that the alkyl chain tether to SWCNT, MWCNT, and graphene surface, presumably through ,r-,r interactions between the carbon-carbon double bond in the alkyl chain and the aromatic rings of CNPs. The hydrophilic polyethoxylate chains extend into the aqueous environment and stabilize the suspension by steric hindrance. MD simulations also showed that Tween-80 molecules interact with the CNP surface via the alkyl chain, thus corroborating spectroscopy results. MD simulations additionally revealed that Tween-80 aggregates on the CNP surface shifted from planar to micelle-like with increasing Tween-80 ratios, underscoring concentration-dependent changes in the nature of these interactions.

Automated summary

Polyoxyethylene sorbitan monooleate is commonly used to stabilize dispersion of carbon nanoparticles such as carbon nanotubes and graphene. However, the mechanism of dispersion is not well understood. This study used spectroscopy and molecular dynamics simulations to investigate the mechanism of stabilization of carbon nanoparticles by Tween-80. The results showed that Tween-80 adsorbs onto the surface of carbon nanotubes and graphene through interaction between the alkyl chain and the aromatic rings, and the hydrophilic chains stabilize the suspension by steric hindrance. The simulations also revealed concentration-dependent changes in the nature of interactions between Tween-80 and the carbon nanoparticles, with aggregation shifting from planar to micelle-like structures.