Curvature and nanoscale forces in controlling self-assembly of carbon nanotube-amphiphile complexes

In aqueous solution, carbon nanotubes (CNTs) bundle strongly via hydrophobicity induced aggregation, yet the extraordinary properties are best realized when CNTs are dispersed as individual tubes. As a result, pure and well isolated individual CNTs are typically desired and extensive effort has been devoted to achieving good aqueous dispersion of CNTs through covalent or non-covalent functionalization. Here, we examine by molecular simulations the non-covalent solubilization of CNTs with a special focus on curvature effects. We employ molecular dynamics simulations and theoretical models to systematically study the amphiphile interactions at the CNT surface. We report that micelle-forming amphiphiles form hemimicellar structures whereas bilayer-forming lipids form tubular coatings. We characterize the energetics of the underlying physical components - the electrostatic, hydration, and geometric effects on CNT dispersion to examine the efficiency of the various CNT solubilization strategies. The observed differences in amphiphile absorption provide a microscopic understanding on the curvature-dependence in amphiphile-coated CNTs solubility in the aqueous phase and will facilitate the bottom-up design of soft nanoscale materials for nanotechnology.