(520f) Computation of Hydrodynamic Properties of Singled-Walled Carbon Nanotubes (SWCNTs) Wrapped in Self-Assembled Surfactant Shells

Single-walled carbon nanotubes (SWNCTs) are materials with structural, electronic and optical properties that make them attractive for a myriad of advanced technology applications. Advancement in separation techniques to sort these materials with increased speed and reliability into monodisperse fractions with respect to their defining metrics (chirality, diameter, length, electronic type and enantiomeric “twist”) has been an active area of research for many years. Almost all techniques currently in use rely on the use of surfactant-mediated dispersion in aqueous media, a step which produces a colloidal mixture in which tubes are packed and individually dispersed in a self-assembled surfactant shell. This protocol prevents aggregation, enabling the separation of individual tubes while preserving their native mechanical and electronic properties due to the non-covalent a nature of the binding. The structure and properties of the SWCNT-surfactant complex are the governing factor in a number of established and emerging separation processes. Understanding how these properties are affected by specific SWCNT-surfactant combinations is essential to advancing separation science and protocols.

In this talk, the structure and properties of SWCNT-surfactant colloidal complexes are studied using all-atom molecular dynamics for a number of bile salt and anionic surfactants commonly used in the experimental literature, with a focus on hydrodynamic properties. The hydrodynamic size relevant in many separation techniques depends not only on the size of the self-assembled complex, but also, to a great degree on the size of the hydration layer  that forms around the colloidal structure, a mechanism which has not been fully understood for these materials. The simulation results suggest that the hydration shell in these systems is the result of a long range electrostatic coupling between the SWCNT-surfactant superstructure and the free ions in solution, with the subsequent hydration of the ions. Understanding this gives us the information necessary to estimate the mass of the SWCNT hydration layer per unit length, and therefore, the buoyant densities the tubes -- an experimentally relevant quantity. Comparison with available experimental data will be discussed.

*Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.