A molecular dynamics study of effect of polyethylene oxide architecture on self-assembly of carbon nanotubes

Carbon nanotubes aggregate strongly to form bundles. One of the ways to control their dispersion is by grafting polymers onto the carbon nanotubes surface. Coarse grained implicit solvent Molecular Dynamics (MD) simulations were used to study the influence of poly (ethylene oxide) (PEO) grafted onto the walls of two single walled carbon nanotubes in water. The system was investigated utilizing both real and repulsive potentials. The chain length and grafting density of PEO were varied to study their effect on aggregation of carbon nanotubes. PEO has an attractive interaction with the carbon nanotubes which causes aggregation, but at very close distances introduces a repulsive barrier which prevents the nanotubes from aggregating. These competing effects are incorporated into the free energy of the system. It was found that the free energy of the system can be manipulated by changing the chain length and grafting density of the PEO. Simulations investigated the importance of individual contribution of nanotube-PEO and PEO-PEO interaction in water, as well as importance of these contributions to the total energy with respect to changing molecular weight of PEO.