Effects of multivalent counterions on the morphology and interactions of polyelectrolyte chains grafted on carbon nanotubes

Abstract

The morphology of polymer chains grafted on nanotubes plays an important role in the effective interaction between these functionalized nanotubes. Herein we perform mesoscopic simulations to investigate the precise morphology of polyelectrolyte (PE) chains grafted on a single-walled carbon nanotube (SWNT) in the presence of added salts. We find that there are two peaks in the probability density distribution for the orientation angle of the grafted PE chains. Increasing counterion valency leads to the height of each peak changing, reflecting the morphology transition of the grafted chains. Our simulations indicate that the counterions with a higher valency induce a stronger collapse of the grafted PE chains wrapping around the SWNT, which strengthens the interaction between the SWNT and the grafted PE chains, and consequently modifies the orientation of these PE chains. The influence of the counterion valency from added salts on the interaction between two functionalized SWNTs is also investigated through examining the potential of mean force (PMF). The results reveal that the PMF between functionalized nanotubes can be effectively tuned through changing the counterion valency. The findings could provide guidelines for fine control over the SWNT aggregation status and may have implications in designing supramolecular nanohybrids composed of functionalized nanotubes and other charged components.