Origins of the Helical Wrapping of Phenyleneethynylene Polymers about Single-Walled Carbon Nanotubes

Abstract

The highly charged, conjugated polymer poly[p-{2,5-bis(3-propoxysulfonicacidsodiumsalt)}phenylene]ethynylene (PPES) has been shown to wrap single-wall carbon nanotubes (SWNTs), adopting a robust helical superstructure. Surprisingly, PPES adopts a helical rather than a linear conformation when adhered to SWNTs. The complexes formed by PPES and related polymers upon helical wrapping of a SWNT are investigated using atomistic molecular dynamics (MD) simulations in the presence and absence of aqueous solvent. In simulations of the PPES/SWNT system in an aqueous environment, PPES spontaneously takes on a helical conformation. A potential of mean force, ΔA(ξ), is calculated as a function of ξ, the component of the end-to-end vector of the polymer chain projected on the SWNT axis; ξ is a monotonic function of the polymer's helical pitch. ΔA(ξ) provides a means to quantify the relative free energies of helical conformations of the polymer when wrapped about the SWNT. The aqueous system possesses a global minimum in ΔA(ξ) at the experimentally observed value of the helical pitch. The presence of this minimum is associated with preferred side chain conformations, where the side chains adopt conformations that provide van der Waals contact between the tubes and the aliphatic components of the side chains, while exposing the anionic sulfonates for aqueous solvation. The simulations provide a free energy estimate of a 0.2 kcal/mol/monomer preference for the helical over the linear conformation of the PPES/SWNT system in an aqueous environment.

Dithiafulvenyl-grafted phenylene ethynylene polymers as selective and reversible dispersants for single-walled carbon nanotubes

“…In a previous molecular dynamics (MD) study, Saven and co-workers demonstrated that poly(phenylene ethynylene)s could adhere to the surface of SWNTs forming a robust helical superstructure. 10 Polymers 1 and 2 were thus envisioned to take a unique ''centipede-like'' wrapping mode to result in highly efficient SWNT dispersion in organic solvents.…”

“…For HiPCO nanotubes, the dispersion selectivity mainly goes to (6,5), (7,5), and (7,6) chiral indices, while some nanotubes with other chirality are also present in the suspension, including (8,3), (8,4), (8,6), (8,7), (9,4), (9,5), (10,2) and (10,3). In comparison with the types of SWNTs dispersed by a typical surfactant, sodium dodecylbenzenesulfonate (SDBS), in water (see Fig.…”

Why do the structural properties of complexes formed by glucans and carbon nanotubes differ so much?

“…As for many other chain-like molecules, such as DNA [36][37][38][39] and organic polymers, 21,[40][41][42] there should be other factors aside from the linkage of the polymers that affect the three-dimensional arrangement of polymer-SWCNT hybrids. For example, It is suggested that polymers with stiff and semi-exible backbones tend to wrap around the SWCNT with more distinct conformations than those with exible backbones, 43,44 which partly supports and rationalizes our conclusions.…”

Functionalization of Carbon Nanotubes with Stimuli- Responsive Molecules and Polymers

“…In these conjugated polymers, arene groups are embedded in the repeat units, which collectively engender strong binding to CNTs via π-π stacking. Experimental observations and molecular dynamic (MD) simulations have demonstrated that the polymer backbones with a certain degree of flexibility would favor wrapping around the CNTs in different fashions [43,44]. DNA or RNA molecules can interact with the CNT sidewall via π-π stacking.…”