Self-assembly of double helical nanostructures inside carbon nanotubes.

We use molecular dynamics (MD) simulations to show that a DNA-like double helix of two poly(acetylene) (PA) chains can form inside single-walled carbon nanotubes (SWNTs). The computational results indicate that SWNTs can activate and guide the self-assembly of polymer chains, allowing them to adopt a helical configuration in a SWNT through the combined action of the van der Waals potential well and the π-π stacking interaction between the polymer and the inner surface of SWNTs. Meanwhile both the SWNT size and polymer chain stiffness determine the outcome of the nanostructure. Furthermore, we also found that water clusters encourage the self-assembly of PA helical structures in the tube. This molecular model may lead to a better understanding of the formation of a double helix biological molecule inside SWNTs. Alternatively, it could form the basis of a novel nanoscale material by utilizing the 'empty' spaces of SWNTs.

Influence of chemical functionalization on the CO2/N2 separation performance of porous graphene membranes.

The separation of CO2 from a mixture of CO2 and N2 using a porous graphene membrane was investigated using molecular dynamics (MD) simulations. The effects of chemical functionalization of the graphene sheet and pore rim on the gas separation performance of porous graphene membranes were examined. It was found that chemical functionalization of the graphene sheet can increase the absorption ability of CO2, while chemical functionalization of the pore rim can significantly improve the selectivity of CO2 over N2. The results show that the porous graphene membrane with all-N modified pore-16 exhibits a higher CO2 selectivity over N2 (∼11) due to the enhanced electrostatic interactions compared to the unmodified graphene membrane. This demonstrates the potential use of functionalized porous graphene as single-atom-thick membrane for CO2 and N2 separation. We provide an effective way to improve the gas separation performance of porous graphene membranes, which may be useful for designing new concept membranes for other gases.

Effect of functional groups on the radial collapse and elasticity of carbon nanotubes under hydrostatic pressure.

The effect of functional groups on the radial collapse and elasticity of a single-walled carbon nanotube (SWNT) under hydrostatic pressure was investigated using molecular dynamics and molecular mechanics simulations. It is found that the radial collapse and elasticity of the chemically modified SWNTs strongly depend on the polarity of the functional groups and the degree of functionalization. The results show that the fluorine modified SWNT (F-SWNT), on which 2.5-5.0% of the atoms are attached to -F groups, can sustain the original elasticity of the intrinsic SWNT, and the pressure needed to collapse the F-SWNT increases by 11.3-21.8%. Functional groups such as hydroxyl groups, amino groups and carboxylic groups can increase the pressure needed to collapse the modified SWNTs, but decrease their radial elasticity. Therefore, the F-SWNTs, due to the higher collapse pressure, are ideal fillers for nanocomposites for high load mechanical support.